yeah i think Im going to have to get one welded. do you know the cost of such a thing?and what i would weld to it? what adapter i mean?
There's a few frame repair companies who can add disk mounts and hose guides. Theres one called Argos Racing I think but try google for 'cycle frame repair/modification'. It wont be cheap though. If you can find the right 'post to is' adapter (alloy one) that will give you the right position for the caliper (see PDF posted by Andy R) you could fabricate something from it. You'd need to strip the anodizing and shape the area that contacts the seatstay to get a good clean fit. You then find a local welder to fit it to the frame. Re-read Andy R's post to see how to correctly position it. You could print the PDF with the dimensions and take that to the welding company so they get it in the right place.
Ive never done anything like this and its at your own risk, maybe worth asking Andy R for his opinion. Only thing is hes away for a while in NZ so you'd have to wait.
Just a thought: Can you get e new rear-end for the I-Drive that already has disk mounts? Theres a few GT fans here who would know. Maybe start a new thread and ask about it?