From what I understand you plan to partially bypass the cooler and mix in that warm gas for reheating further downstream, right?
I see one problem. The bypassed gas misses the oppertunity to shrink and drop its moisture.
I think the easiest way would be just to steal exhaust heat on the way up front. I think I will weld a new muffler with two extra pipes in it. One for air preheat and one for gas reheat.
Ops, there you drawing popped up.