OK, so it sounds like your workarounds are working for you, though you're still at a bit of a disadvantage compared with someone who has feeling in their thumb.
I guess you have two things to consider. First, what's different about the pieces you're working on now? It sounds like you have more than a couple of quite tricky lines down already. Maybe see if there's some particular string crossing you need to look at or some such challenge that your other pieces don't have. Second, as nearly everyone has said, self-consciousness kills music. Can you find a way to focus on the piece, not what you're doing to it?