I used my dinghy's outboard on the boat once, when I had a cooling issue on the inboard engine. I lashed my Zodiac RIB with a 9.9 Honda on the starboard "hip" and was able to motor about seven NM into the harbour, although the tendency to curve to port (I had to offset the outboard tiller a touch) plus the extra beam made docking a little tricky.
The outboard was definitely overloaded by this, however, and got quite hot. I didn't actually sit in the outboard while it was doing "tug duty", but got my wife to steer while I sat on the rail, ready to kill the throttle or to vary the speed. It was dead calm at the time, which is why I didn't just sail in.
So while it wasn't a fuel problem per se, it showed me the utility of having enough outboard power to get the boat moving. We were able to make 4 knots under the RIB/outboard power, which was pretty decent, considering the boat itself is 10,000 lbs.