Shrink/reset directory size?

Is there a way to shrink a directory entry?

My dovecot maildir directories have increased in size from the default 4096 to several megs, and it is messing with disk quotas.

The only way that I have found, is to delete and recreate the directory. I am hoping there is a magical function somewhere - I am open to anything, except for hand-coded assembler.

Edit:For posterity, to find dirents>4096:

 find / -type d -size +4k -printf "%s\t%p\t%i\n" | sort -nr