PPT/PST are basically codeine and morphine, mostly codeine I believe, so they don't have as long a half life as methadone or buprenorphine. There is a lot more in PPT/PST than just those two compounds, but those are the most important for our purposes. Using buprenorphine to transition off methadone works really well, because you're only using it for 2-8 weeks, and using a short taper off that makes the transition really easy. Of course tapering down as low as possible will make using whatever else you can to get off it a lot easier.
Because methadone is long acting, all that means is it has a longer half life and the withdrawal will be prolonged than compared to something shorter acting like codeine, morphine or heroin. But if tapered properly to a mangabey low dose (which you do not necessarily seem to have the luxury of doing in this situation) the withdrawal off longer acting opioids is less intense than short acting ones, and longer acting opioids are easier to taper down to smaller doses than shorter acting ones (there are a number of reasons for this, but basically it is that there is less need to redose with longer acting opioids).
If you've been around where you are at now for over a year, it is going to take more than just two weeks to use another opioid, whatever the nature, to taper as comfortably as you could. So what I am trying to say is that, given your situation, you could end up being fairly uncomfortable during when you jump off methadone onto another opioid, and especially when you jump off all opioids.
Whatever type of opioid you use to ease the early acute withdrawal of methadone, which isn't such a bad idea at all IMO (at the end of the day it doesn't matter what it is, although you ideally would want to use less habit forming ones like tramadol, codeine or buprenorpine), the idea is not to take it long enough to create a new dependency on the opioid you use to ease the methadone withdrawal.
If you use a longer acting opioid like buprenorphine that you are not now dependent on to make the transition off all opioids, it will ease the transition when you stop taking the replacement long acting opioid (buprenorphine) because it will stay in your system longer. Because you haven't developed a dependency on it yet means that your body will continue metabolizing it in very small amounts for longer period of time after your stop taking it than shorter acting opioids.
I high recommend stocking up on comfort meds like kratom, gabapentin, baclofen, clonidine and a short corse of a longer acting benzo like clonazepam or diazepam to bring with you on your trip. That will make it a lot easier when you stop taking whatever opioid you choose to jump off methadone with, because when you stop taking the replacement opioid, your body will still be going through methadone withdrawal. You will still need some for of support if you want to remain comfortable enough, in my opinion, to be fully functional.
If you have to power through the prolonged methadone withdrawal without anything useful to supplement the lingering withdrawal, such as inmates in prisons often are left with having to do, you can totally do it. It will be much more of a challenge, but it is still doable.
Good luck! Sorry for the long ass post. I had a bit of a hard time answering your question for some reason.
EDIT: Ah I forgot you have two months before you trip! This is good news! I'd highly suggest switching to buprenoprine for 2-8 weeks, or better yet taper down the methadone a bit further. If you don't feel like tapering the methadone anymore is going to work, you can always switch to another opioid.
Maybe try tapering more for a month on the methadone then switch to whatever replacement opioid you want to use for the last month before your trip. You can use the aforementioned comfort meds to easy the end of your taper on methadone. IMO it would probably be significantly easier to jump off of <20mg than over.
Since quitting the pods three weeks ago I've been utilizing my newfound heightened sensitivity with music. If I get the right track with the right mood, it's so gorgeously euphoric. 