Well, here's a thought. The onboard charger in your car has no problem with 277v, so yes, you could use that power. You could also have the electrician install a NEMA 7-50R, and you've covered that part... 277v / 50a available from the wall. Under no circumstance would I recommend using the NEMA 14-50R on this higher voltage, as somebody could plug something into it that won't like it!!! It would absolutely SMOKE the electrics in a motor home which would normally use a NEMA 14-50.
So, it's connecting the two that's a problem. To my knowledge, every EVSE on the market (including UMC / HPWC) is limited to 240v +/- 10%, which is 264v max.
You could build a custom unit from an OPENevse with electronics to handle 277v. Or, test out a cheap EVSE to see if it goes up in smoke at 277v?
To do this experiment with any "plug-in-the-wall" unit, you'll need an adapter from that plug (say, a NEMA 14-50R) to the NEMA 7-50P.
Be cognizant that 277v and a neutral is not the same as two 120v lines that make up 240v. It is something that can be done, but the easy(er) answer is a somewhat expensive transformer, as suggested above.