Well. losing weight should help. Fat tends to be subcutaneous and it is a great insulator. So the thinner you are, the easier it should be to vent off excess heat. I lost about 20 lbs since last year and this year seems noticeably cooler to me. It might just work. But you do not want to lose weight really fast. Fast weight loss is usually muscle weight and not fat. One can lose fat fast if you are careful with your diet (adequate protein and carbo) and you exercise like all get out.
If you can, just start as early as possible to "beat the heat". Drink cool drinks during the ride and hope.