I took a cpvc 3/4 in 90 degree elbow and used a dremel to cut a groove in the bottle so that it will slide over the feed tube on the pgp.
then cut a piece of 3/4 in (i think) copper piping about two inches. A viewloader hopper will slide right onto the copper piece. a little black electrical tape will hold it in place.
I then took off the front plug by unscrewing the sight screw. Cut a piece of wooden dowel (i think 1/2 in) to slide right in up to the spot where the ball falls into the chamber. Painted the end of the dowel black and used a screw throught he site screw hole to hold the dowel in place.
Only problem is holding the whole thing on. If you cut the cpvc tight enough that works. or I used electrical tape around the whole ball tube and elbow. Not a pretty but works also.