If I multipost, it's usually due to some regrettable circumstance like phoneposting. I used to mod two different Invision forums. Merging multiposts is superior. I'd take it even further.
Suppose posts A, B, C. if A and C are by the same poster and B doesn't reference A, I'd merge A and C. I would also apply this pattern to higher degrees of separation than the one post between A and C.
This policy substantially increases the needed amount of janny effort though. I always want to be kind to jannies. I know the gig. Still, though, clean forums are every poster's best interest.