I'm still working on this. I haven't dropped off the face of the earth; it's just taking a bit. The way I wrote the original define-macro macros, they called some functions (passing in symbol names) to generate blocks of code. This technique essentially depends on variable capture, so I can't really do it with syntax-case (at least not without twisting things into an obscene shape).
Anyway, the transformations aren't terribly difficult, they just involve a lot of hand-rewriting to turn all the function calls into actual macro expansions. I think I'll be done reasonably soon.
