Is there any way of knowing the name of the current file, so you can include stuff based on it?

Not in the current version of fasm. You could make you version and add something like %currentname% for text replacement.

Although I don't see where this is useful, perhaps you can post an example?

I was thinking this might clash with SSSO anyway.

I'm trying to develop a system for including symbols in debug builds, and thought I might generate include files from .fas files that I can build the debug versions with.

A better way would probably be to build debug versions automatically outside of IDE:

generate symbols
extracts wanted labels from .fas
inserts these symbols in assembly file and changes it to debug mode
compile resulting assembly file