Could put it up on the audiosurf radio for a day, but that may require expensive licensing.
Yeah, I sat down and thought about something like this too... you could always get around the expensive licensing by actually having unsigned bands music up for download. That way, they could get some more recognition and we'd get some interesting, fresh and new music circulating on the internet.
There's also other options, but I think this one has the most potential. As for hardness, I suggested a range for traffic already I think. 170 to 270 is seriously a good zone, anything above that isn't worth it.