It's not easily done if you have an Auto-Inject style case with the plastic center Fan/Speaker assy. Howevcer IIRC only one of the grilles is obscured by the later type boards, so maybe you can fix the fan over the speaker grille and put the speaker somewhere else (Note: NOT right up close to the floppy drive!!).

Oh, just incase anyone cares there IS a tutorial for this - I wrote it. It's here:

http://www.68kmac.org/articles.php?id=32