Okay guys. I got it. I came up with a way to launch about 20-30 paintballs withought cartriges and withought having to replace wadding every shot. The secret is a built-in sabot in the barrel, a lip on the barrel tip to catch the sabot and not the paintballs, and venting ports near the tip of the barrel.
Lets say you have a 2" barrel and want to make it into a paintball barrel. You take a 1.25" endcap, 1.25" coupler, 3/4" of 1.25" pipe, and about 4 inches of 1.25" pipe and glue it together. The 3/4" chunk goes into the open end of the coupler. Glue a rubber gasket the same size as the open end onto the coupler and 3/4" long pipe to act as a shock absorber. This is your sabot; it will fit right in the 2" pipe.
Now put a stopper screw(s) on the chamber side of your barrel to stop the sabot. On the other end you need to take a 2" cap and drill/dremel out the entire center of it until it has a hole with a diameter of about 1.3". It can be bigger, just not 2". It needs to stop the sabot and not be so small that it can get in the paintballs' way. On the inside of the muzzle stopper there needs to be another gasket for shock.
When this is all done you need venting holes near the muzzle. Do this by measuring from the muzzle to a few inches more than how long your sabot is. It should be about 7-8 inches. Drill many many large holes for about 5 inches back. So there should be a lot of pipe missing 7-12" from the muzzle. It needs to let all extra air out and be able to withstand the momentum of the sabot only. The further back the holes go, the less momentum it will have when it gets to the stopper.
When operating all you need to do is find out how many balls fit in the sabot and just pour that many down the barrel (not straight down) or if the sabot is still at the muzzle it makes it easier. The barrel must be held upwards until just before the shot. If done correctly the sabot should slide down by itself and may just require some sanding to fix. To take the shot lower the barrel and fire immediately. The balls fly out and all you need to do is fuel and pour balls in.
Edit was to get rid of the damn green text!