I've never tried using play-doh for a mask...or in this case, play D'OH!.....ha, see what I did there? Come on, it was a little funny....
Any how, if I ever need to mask in a similar fashion, I use a kneaded eraser. You know, those putty-like erasers that are usually blue or gray in color. It can be pulled apart and shaped in exactly the same way. It leaves no residue that I've seen and isn't sticky.