Hi Ben.
Regard such a landing as a forced landing without power, make a Mayday call, Squawk 7700, and think of what little power you have left as a bonus that you might loose at any moment.
MJ
Ps. I'm assuming that you don't have enough power to maintain level flight at a safe speed, as in that situation the best option would be to head for the nearest airfield, at the same time preparing for the possibility of a complete failure. In that case it would be appropriate to send a PAN message, and Squawk 7700, upgrading to a Mayday in the case of further loss of power.