I was thinking that a problem with this might be that each sendmail daemon would need starting with different parameters, but the vncserver initscript handles the equivalent of this in quite a neat way. How about raising a Request For Enhancement of the sendmail initscript in bugzilla?
I believe the initscript system is something that's going to undergo a lot of change in FC5. There was some recent discussion on the dev list about this, pointing out that we can't use Sun's system for licensing reasons.
Meanwhile, does anyone have a working patch that would do this, that could be attached to the bugzilla?