Comment #14 on issue 3108 by [email protected]: Patch: Better staggering of accidental placements.
http://code.google.com/p/lilypond/issues/detail?id=3108
I think this patch is OK for countdown even in light of the potential feature Werner is talking about. It'd take 15 minutes of work to accidental-placement.cc and accidental-engraver.cc to allow the user to do what he's talking about - it'd just mean expanding the functionality of the accidentalGrouping property.
