[plt-scheme] Transformer environment and identifier-binding: revisited

I think I've run into an issue similar to the one discussed a couple years
ago (http://list.cs.brown.edu/pipermail/plt-scheme/2004-March/004911.html),
in which `require-for-syntax' shifts runtime bindings to the transformer 
level, complicating `module-identifier=?' matches to constants.

My problem does not involve `syntax-case' -- I simply need to know if a
given identifier is one of the built-in arithmetic operators (e.g. `+').
Can I instead accomplish this by checking the `source-mod' and 'source-id' 
fields of the list produced by `identifier-binding' for module-defined 
identifiers?

Is passing a suitable binding into the required-for-syntax module still 
the best general solution?

-Casey