One excellent way to portray visual humor in comics is to illustrate people's thoughts. I do this all the time in Think Before You Think, mostly because it's all about people's thoughts. I've seen it done on TV, too, where it cuts to someone's thought process in the middle of a conversation, just for the sake of humor.
I like using mental cuts for a lot of reasons. For one thing, since it's not real, anything can happen without it actually happening, and this is a vehicle for absurd, exaggerated humor in a relatively realistic comic.
And of course, since there's a mind-reader in Think Before You Think, these scenes can flow seamlessly into the conversation without anyone having to explain their thought process.