It does look like a tough problem, but not that hard to solve. FAT is very simple in how it works, so translating it to something else on the fly really oughtn't be a horrendous issue.

Tricky, yes.

EDIT: Sometimes I (wrongly) wish I weren't already so busy here, as this would be a perfect sort of thing to work on otherwise. Kinda like how Hijack was, back during the 2001-2002 tech crash.