Is there such thing as a transit visa? I'll be flying out of Bangkok in May, and I'll have to do a visa run / trip to a nearby nation shortly before then. I'm debating how long I want to stay in Thailand on the second stay until my flight leaves. Is it viable to just come for a few days on a special transit stamp, or will I need to come in 30-days visa exempt again (US passport)? I want to minimize my number of 30-day entries because if I do that many times, I fear they'll stop letting me in.

(I know I could just change my flight, but I booked through one of those annoying services where you have to pay a bunch of money for them to help you at ALL, so I'd rather not do that. Lesson learned; never going to use that site again...)