I havent tried it but as you prolly know already,bupe blocks out the effects of other opiates,so i guess this applies for done too.No matter how much heroin for example did i use when i was on 8mgs of bupe,there was no effect.Unless im missing something,i dont see why methadone would be any different.
But why do it anyway?Both drugs are maintainance drugs and most ppl wont get high off either of them,especially those who use or used to do strong opiates(H,oxys etc)..