you could shave him down but if he never was shaved it may be a shock to his system and if you choose todo that i would not take him that close to skin
I know it's an older thread, and you've decided not to shave him, but I thought I'd throw a couple suggestions out there for you to help Charlie beat the summer heat...
Canine Cooler Beds - This may not be an option if Charlie is a chewer: http://www.petstreetmall.com/Canine-Cooler/1954/1474/
*I used to use these when I'd take the dogs out during the summer - I'd put them in the bed of the truck (it was covered with a camper top) and it kept them nice and cool back there.