I too have the Camelback rogue - never bothered me that it was on my back but 30 yrs of scuba diving makes a camelback feel like a feather....
I did learn a good trick though - I half fill the reservoir, seal it up, and blow air into it via the tube to make it balloon out. Then put it in the freezer overnight (or just keep it there till I need it).
Then when I'm ready to ride, I take it out, and fill the remainder with water (filtered). You will probably have to run some hot water over the opening to get it open, and also where the hose enters the bottom of the reservoir to make sure the path is not blocked. Result - I always have cold water, but not too cold. Even on a 40 mile ride in very hot weather I still had cold water at the end. Having the "ice" probably helps to keep the unit a little cooler, so it's not hot on my back, but there is enough insulation/padding in the camelback itself I think to prevent it. And the ice seems to last several hours. If I'm on a really long ride, and it's really hot, I have been known to stop and buy a bottle of water, and top off the Camelback just in case.
My only real complaint? The first sip or two of water on a hot day is HOT! UGH! I have been known to just spit it out so I can get to the cold water. I've seen neoprene sleeves for the hoses but wondered if they were enough to prevent the excessive cooking of the water residual in the hose?