Adding carbon stays to an aluminum frame requires a lot of additional work for little benefit. You need heavier alum end bits, epoxy (usually flexible), and you run the chance of corrosion. I looked into this for my frameset but I couldn't see benefits so I skipped it. For me cost wasn't an issue - I wanted significantly lighter, more efficient (stiffer), or (as a side benefit) more comfortable frame. I couldn't get any of those with carbon add-ons.

cdr