It's probably been done before but anyways...
I made some custom soundeffects. Mario theme. (Well made and made, I just downloaded some .wavs of the internetz and put them in a folder.)
You can get it here
www.knark.de/xxx/other/audiosurfmario.rarSize is 2.2 mb. RAR file. It contains a folder named sounds that you replace one of the existing soundeffects folders with, and a readme describing in more detail how to do so.
The sounds themselves are mainly from supermario with a few from sonic and altered beast.
You replace the files at your own risk.
If anyone has any interesting custom soundeffect themes feel free to post them here.