If one can remove the original box, then suspend a new single gang ring with Madison Bars or a block out from a nearby stud, then Daniel's plate would work.

Ideally a screwless 2G -> 1-G adapter plate exists somewhere.

Visually, it may be best to find an excuse to add a second device to the box and use a standard 2-G ring.

While I don't like them for this sort of application, a blank Decora insert is another path.