What about if you taper for a week with the stuff you're snorting, then a week with the methadone pills you've got, line this up to finish on a Wednesday night or Thursday morning (methadone has a long half-live, Wednesday would be better) try get through work on Thurs & Friday, even if you can't sleep Thursday night, then you've got the best period to actually withdraw on the weekend (I assume that's what you mean by two days off) and hopefully will be manageable by Monday for work. This might not work of course, I've tried this a bunch of times. Unfortunately the opiate I'm addicted to has a long withdrawal profile, similar to methadone but shouldn't get like that with using 160mgs to taper.