Since you want to stop the methadone, you could instead try to very slowly taper off of it with the doctor's recommendations. Or you could try the Butrans patch and take if off if you have withdrawals. I understand that the medication will last at a lower dose about 48 hours after you take it off.
I don't blame you for your fear of precipitated withdrawals. Even though you're not an addict, you may get some good information by posting in the substance abuse forum as there are people there who have more experience transitioning from narcotics, especially methadone, to bupe.