I work with it every day, so a lot of interesting ideas have crossed my mind....
One thing I want to do is to take about as many expandable repair couplings as I can get a hold of (url=http://reticonline.com.au/cw135/images/large/slipfix_LRG.jpg]these things[/url]), stick them all together, make some way of compressing them all together in one big motion, and see how far I can shoot a plug.
If you're really bored and have $10 to waste, grab 2 or 3 of those things, glue them together, glue a cap on one end, and buy a handful of plugs for the other end. You can shoot the plugs pretty far, depending on how many couplers you have.
PVC playhouses are pretty neat... You can make large ones pretty cheap using tarps as walls and a roof.