[CentOS] an rsync question

Is there any way to have rsync compare against a file with a *different*
name?

What I'd like to do is compare a vm - whatsit.img against a backup -
whatsit.current, that's a symlink to whatsit.timestamp, and if different,
*then* make the copy (which my script will then move to
whatsit.newtimestamp, and change the symlink to point to the new one, then
remove the old (or maybe save an older copy or two).

So:
backupdir
  \ whatsit.20130101 (backup of whatsit.img)
    whatsit.current -> whatsit.20130101
    whatsit.20121201

After script w/ rsync
backupdir
  \ whatsit.20130201 (backup of whatsit.img)
    whatsit.current -> whatsit.20130201
    whatsit.20130101

     mark