The obvious

That would make things certainly more interesting, even if it doesn't include introducing a new main character and the only point of a random McMillan coming in is to motivate Jon to get out of bed to throw them out and get some privacy. And to see how short he's gotten :P Another obvious person to bring in other than Sarah would be Roxanne's boyfriend (if we assume that she has one). I feel like that would be too early in the story to have Jon experience hetero sexual things. Let's let him struggle with his body and be confused for a while :)