[Mr. Freeman]

I was playing with a water balloon launcher at a party today. Long story short, the max range on the thing was about 10 feet, but I learned a few things.

Lubrication for the balloons is a must. Water doesn't work. It beads up and leaves most of the barrel completley dry. I suspect this is due to surface tension, thus, soapy water might work but we didn't try it.
Some type of cooking oil might be a good idea. It should lubricate the barrel as well as be safe should someone manage to ingest some of it or get it on their skin.

There should be some way of draining the pressure chamber. If the balloon breaks in the barrel, the water will drain into the pressure chamber.

Backspin seems like an impractical idea. The only reasonable way I could see to do it is to not lubricate a strip on the top of the barrel. This might also cause the balloon to break though.

Post pictures of this thing once you've completed any modifications. The wireless control system sounds pretty cool.