I've been known to go to the trails in the summer with a gallon of water, and throw it on my body so that it takes a long time to dry off. It keeps you cool.
Proper hydration, and very careful hydration, will keep you on target. Infact, if you keep hydrated, there isn't much your body isn't capable of, hot weather or no. Your body will maintain a homeostasis, but watching your blood pressure/heart rate will let you feel for how much activity you should do.
It's hard when there's no retreat to the A/C if it gets to be too much, but don't forget about the "Cold water" function on your shower that everyone else never touches!! A cool, lukewarm shower after a hot workout will leave you feeling refreshed as well.
Lastly, have you thought about a bit less cardio and more strength training? Strength training doesn't require a lot of the 'heating up' on your entire body that cardio and plyometrics does, so push-ups will make your arms burn, but the rest of your body won't suffer from the heat so much.
Also, early mornings and late nights are the cheapest ways to exercise in the cool air. Just adjusting your routine and schedule to avoid the hottest parts of the day will keep you from overheating. I don't recommend (Especially in texas!!) working out outside at 3pm, for example. It's the hottest time of the day here.