I've been reading alot of your info out there on bubbleponics and then I ran across something in a book...
If I've got this correct, one of your big pains in life is the res being heated up by the pump. One could put an external pump that draws water up a tube to the pump then deliver it to the plants but you'd probably lose some of the oxigenation with all that travel and the pump would still impart at least some heat to the water.
Here's what I read. It was in "Hydroponics, soiless gardening explained by Les Bridgewood". If you take a tube and push it down into a body of water then place an air source below that tube you have created a "foam pump". It works like this. The air stream (I'd think from an air stone) flows up the pipe mixing with the water in the pipe, lowering the density of the water. That makes the water pressure from the tank force more water into the pipe and itself getting air mixed etc. Causing the foam in the pipe to be pushed up and out. Put a 90 degree bend on the pipe top to direct it. Does this sound workable in your systems? With a little experimenting I'm sure it could be made to deliver just about any GPH to simulate the current pump version without the heat. Or has this been done already?