Please excuse the frustrating undertones as I have attempted to get this set up correctly multiple times to no avail (possibly and most likely due to my ignorance, but also
I maintain a gitosis config at work, and when a developer has multiple ssh keys, all I have to do is put all these keys in the same keydir/user.pub file.
So concatenate all your keys into keydir/benny.pub and you shoud be all set.