People generally say to stick him on a BB and do it that way, but there is a problem:
At low levels, he won't get nearly as much xp as the rest of the crew. If you have
some time, some crew that aren't TOO fat already, wouldn't this seem plausible-

Run him in a DD at lower levels, doing DD-only rooms. Higher level gunners will
definitely help here. Also, DD rooms/Blitzkreigs have a pretty high turnover rate,
which helps get his level up.

At progressively higher levels, bring him along in a CL, then a CA. Since your other
BO can probably use a decent version of each, this works out fairly well, in theory.