To clarify what Adrian said: the ni compiler does stop after generating the I6 file.
You could modify a command-line script to insert an extra step between ni and inform6. (See thread: Command-line Inform 7: how to use ni, inform6, and cBlorb by CLI)
You could also do this by replacing the inform6 binary in the IDE with a shell script which modifies the source and then runs the real inform6.
(This is harder on Mac, though, because of app signing. Worst case, you could rebuild the IDE yourself: https://github.com/TobyLobster/Inform .)