Originally Posted by groth

If it were me, I'd try to make the pedals and seat have the same geometry as the spin bike. Same crank length, the cages, and the same seat height and set back. This might require crank shorteners (or just shorter cranks) and also might require a set back seat post. Then I would raise the handlebars and/or shorten the stem, to take the weight off the hands. This would probably put you in a more upright position than you were expecting, but if it works you can gradually lower the bars as you gain strength in your back. Also, there are bar ends with various geometries including some that go straight up (or whatever angle you want) from the ends of the bars and some that go up and then in.

Good luck!

- Ed