Would it be a safe bet to take a regular POP-R and put some distance between the back dressed treble and the body of the lure?

Saw someone do this sortof thing with a HULA Popper once. They tied a small wet fly to the back with about 6 inches of leader and did pretty good.

Don't know why not.  I'd opt for something a bit larger than a small wet fly though.  Perhaps a larger streamer-type.  That would emulate a minnow chasing the relatively small Pop-R.

The only doctoring I do to the Pop-R is to sand down the front lip, but I like the idea about the back hook.

Sure it will work.  I have tied a small crappie jig to the rear hook of a Pop-R and had some success.