If it's a moonroof, and doesn't actually move, tilt, etc., get piece of glass from a junkyard CRX (or hatchback?) and see if it's possible to get it bonded in place with urethane windshield adhesive. It won't go anywhere then. It should be easy if there is a flange under where the glass sits, just something to bond the glass to.. You can then bond a trim gasket in place with weatherstrip adhesive.