You could buy a carrier designed for a piston system. They don't have gas keys, but they do have a nub for the charging handle to grip.
Still, to be on the most legal side, build a dedicated "straight bolt" rifle. A side charge design would be nice for the rapid/faster reloads.
If you wanted to be on the tricky side, build a piston upper. When you hunt, turn off the gas and remove the operation rod. It's a 5 second swap. The rifle won't cycle without an op rod.