There was an invention proposed in 1972 before electric trolling motors came along, one that might have inspired what we enjoy today. It was an attempt to avoid the noise from typical gas powered trolling motors. I found a patent description with illustrations, but you will soon detect it would present more problems than solved. You might find a way to McGyver it to attach your trolling motor to your outboard housing. Click Here
That's a PDF document read in Adobe Acrobat, a free program. The link came from Click Here
Good luck. It looks like the idea didn't take off.
I have an idea for you to chew on. Mount your trolling motor to the side of the outboard, then put a tie rod between the two so the outboard steers the little motor. Make some sort of 2-way mount to allow the motor to be pulled out of the water while the outboard is in use, and swivel side to side. Going to that much trouble you might as well come up with a tiller bar used to put the trolling motior in and out, using a trigger on it that operates a pin that locks the motor into various horizontal as well as vertical positions.