J.C.
I'd look for the small A/C units, which also dehumidify (search for "portable air conditioners" - here's a link to info: http://www.consumersearch.com/www/house_and_home/portable...)
but you could also try opening his door after he falls asleep, at least temporarily until he gets used to the idea. Also, a window fan turned to "exhaust" will pull the cool air into the room in the evenings before he goes to bed.
Other things you can do - put darkening shades or curtains on all windows that get a lot of light during the day. Put a big fan in one window of the house to pull in cool air after dark (and make sure one window has a fan turned the other way, to exhaust air out.) You might also want to put a thicker crib mattress pad on (the plastic is sweaty.)