I don't have any real knowledge to add to your question as I went with TT for my chip (currently stock) - I would imagine if TT doesn't do it, there is a good reason.
Just for conversations sake, and to maybe get some more attention to your question - maybe do an 86-87 ECM swap and then have the ability to have TT make a chip for 42.5+ (when you eventually upgrade), have scanmaster ability, etc? If I ever plan to go harder with the HA, I think this would be the route I'd prefer to go and open up a few more doors than we currently have open? Again, just stating/asking for conversation sake.
Your only option is to convert to the 86/87 ECM. While you are at it convert the coil mod and coil pak and get a translator with LT! MAF. Your car and you will be a lot happier and your wallet lighter. I went down this road before.