I suggested this already...but was only regarding crafted stuff. Working exactly like a common local leve. you give the maths, set a reward and if anyone actually accept it you get the even amount of crafted items you game mats for.

I also posted the idea in my blog here a few days ago...i wrote there pretty much the very same i suggested them...but incase you feel like checking, be warned its just a wall of text occasionally having some math and examples...nothing good to read unless you like discussing game mechanics =P