Sorry, I don't know the answer to your question, but I have a suggestion which might help.
The CodeWarrior assembler also has an incbin statement, so you could add a small assembler file to your project along the lines of:
.data
.globl _myData
_myData:
#ifdef foo
.incbin 'file1.bin'
#else
.incbin 'file2.bin'
#endif
From C, the data would be refered to by the symbol 'myData' without the leading underscore.
Hope this helps
Simon