I added server matching ProxyPass and ProxyPassReverse entries, but I was getting "already used by another worker" [warn] messages upon start up.
I have a proposed solution that's good enough for me, since it appears to have cleared up the messages and pretty much made me forget about this problem. This solution is to put the entries in reverse-case order in the config file.
I think the real issue had to do with expression matching, since if "Videos" was listed before "Videos2", there was a warning. Once I reversed these entries, the warnings stopped.