If your going to do a ben10 eiken crossover, might i suggest that the human girls are mixed in with the regular eiken cast, the aliens are a part of a new cross culture student exchange and ben is a student given the job of peacejeeper slash representative. Everyone has eikien proportions. That way you have conflict, a goal and a reason for everyone to be there.
Also there was a 'milkbender' comic a while back, is that what you meant?