I live in San Diego too, but in the coastal region. So I'd say the heat is much less extreme during those particularly hot and sticky months. However, growing in southern California is, while not quite the "holy grail for tropical gardeners" that south Florida is, still fantastic for orchids.
I don't think you need a greenhouse. You can block the hottest sun of the day with shade cloth if that's what you're worried about. That's what I'd personally do if we actually had a yard to put anything in.
What I've always thought would be neat to do is get one of those outdoor canopy things that people buy to sit under, apply shade cloth as needed, set up some shelves and a chair and I have an outdoor orchid oasis for me to enjoy.