In the event you decide to look at hydration packs, take a look at Deuter. They're german made and are, in my opinion, cooler (from a heat standpoint) than the camelbacks. This is the pack I own:

http://www.deuterusa.com/hydro8.html

What makes them run cooler is their air stripes system. It allows for air to circulate on your back unlike the camelbacks that I've owned in the past.

http://www.deuterusa.com/airstripe.html

The other thing I like about the deuter is their bladders. It uses a clip which is removed during cleaning or filling of the bladder so you have full width of the bladder for access. Adding ice is easy

Mel