I have often thought about doing the same thing you are proposing.
When I was cruising, I had a 25 HP outboard for my dinghy. I thought it would provide plenty of emergency power for my 42 foot boat (not to mention it could even be a lifesaver with a broken rudder) if I could figure out a way to mount it.
I haven't done it yet, but I keep thinking about using something like this.
So that if necessary, I could merely mount the motor on it, and then lower it to where it could power the boat. I have a swim platform on my boat that would allow me to reach the handle and steer it.
Like I said, I haven't done it yet, but I often think, why waste a motor and just use it for the dinghy?