I've seen various efforts at such a backup plan.. should work and other than the throttle you can steer with your own rudder for the most part.
After a a series of persistent fuel starvation issues a friend with a Hunter 37.5 just built a ladder mount out of 2x4s, essentially, that should do in a pinch - just in case.
If you can handle the aesthetics, I've seen a standard spring-loaded retractable OB bracket mounted as low as practical on the transom for just that eventuality. Also Chrisncate recently built a transom mounted bracket that you can slip an OB mount into.. see here:
The final solution - what I came up with regarding auxiliary propulsion (pic heavy)