You have gaps in your thesis. Big gaps. You want to fill those gaps with something meaty and impressive. Your time is running out. Hey, don't despair! There is something you can do: Run away. I mean it: Run away to a top lab where there's an expert who makes what you are struggling with look easy. I've gone absent with leave a couple of times during my PhD. Each time I've been warmly welcomed by the people in the lab I've been visiting and had a successful trip. It's broadened my horizons and given my research a shot in the arm.
Spending even a few days in a lab in a different part of the country might sound like an unlikely way to get your research moving. But many PhD students have to undertake short trips to the labs of their industrial sponsors and from what I hear these essential secondments can be incredibly useful in giving a fresh perspective. Just because you're not industrially funded, though, doesn't mean you have to be stuck in the same university for 3 years. And unlike those CASE students, you have a choice in where you end up!
Take it from me, you can get more results, faster, than by staying at home and putting in months of backbreaking effort trying to get a potentially nightmarish technique to work. You'll find, to your surprise, that most of your fellow scientists will happily accommodate an extra PhD student for a week or two. Really, all you need to do is ask nicely.
One spin-off of your trip will be that you'll broaden your mind to different ways of doing the most mundane lab practices. For instance, they might do strange things with their disposable plastic-ware, and their instruments are probably unrecognisable. It really opens your mind to realise there is more than one way to get the same result: There are no paths set in stone in science, only good practice. You'll soon find yourself picking up new ideas and adding them to your ever-growing "toolkit" of lab skills.
So, if you fancy an expenses-paid trip to visit another lab, just follow this simple four-point plan:
Step 1. Find something that you cannot do. (Let's face it, this should not be difficult for any of us!) If you cannot find anything suitable on your long list of overdue experiments, perhaps you should think up a new one, one that might add something extra to your PhD. You might not be currently stuck in a rut with a tricky technique, but I still recommend "playing away" to have a crack at something really challenging. It'll probably impress even if you don't quite pull it off. There's nothing wrong with purposefully looking for a "ticket" to another lab. The message: You don't have to wait until the need arises--invent the need!
Step 2. Check carefully that there are no resident experts where you currently work. You'll just have to ask around and follow-up the inevitable trail of people. I know it's a shame, but from your advisor's perspective resident experts tend to invalidate your need to travel. At least you might satisfy your boss that the only person who's tried fluorodynamic quasi-quantum spectroscopy at your place hasn't done it for years and never got it to work properly even then.
Step 3. Find an expert, preferably in a prestigious lab. Let's assume you don't already have someone in mind from one of those semi-fortuitous encounters at a conference. Expand your search using the same high-flying skills you used to check for in-house experts--remember that's just talking to people and sending lots of polite e-mails! Refer to my article on setting up collaborations  for guidance on etiquette. (As an aside, these noncollaborative trips have a funny way of ending in useful collaborations.)
Step 4. Book your train tickets and go to their lab to either do the experiment or to learn how to do it.
To help counter too many discomforting feelings of unfamiliarity and homesickness, take a few bits of your own lab kit with you. I took this concept a little too far the first time I experimented away from home. I arrived with a massive box containing everything I might need, right down to the last precut strip of laboratory film. My co-workers were possibly a little impressed, but certainly surprised, at my over-preparation.
When you arrive as a visiting worker, don't be surprised if you experience a sudden feeling of liberation. After all, you're away from the watchful eye of your boss and postdoc minder. But don't get sloppy! You need to get as much as you can out of this trip and it might even turn out to be a working interview. There's no better way of advertising your skills than going to work in a top lab right under the nose of your ideal postdoc advisor. Even if the group leader is office-bound, word of your aptitude will soon get back to them and job offers are not unheard of! To enhance the value of your trip, make sure you go prepared to give a short presentation. This is often expected of visiting workers, even if they are only around for a week.
One last word ... You have to be the resourceful type to make this sort of venture work. If you arrive expecting your temporary colleagues to do all the donkey work and just hand you the results at the end of the week you could be in for an uncomfortable time. And you won't be able to claim the work as your own when it comes to writing up your thesis.