It is not easy to find an answer. Because you or somebody should sacrifice his adapter:) It's a recent thing and not easily break.
But I have an idea. Clip a cable-tie horizontally to your adapter. Cut the tie end a little longer enough to drill and hang to your key-ring. a 5 mm tie width with a 2 mm hole would be good for the purpose. I cannot add a photo but cable-tie holds the device firm enough. Maybe a drop of proper type of glue will secure more.
If you don't like it, nothing is harmed than a cable-tie!