Combining keyboards and festival toilets, the two dirtiest things known to mankind, only seems logical. This could have spawned new lifeforms.
[1] http://www.copperkeyboard.com/
[2] http://www.tripadvisor.com/LocationPhotoDirectLink-g1575479-...
But maybe you could cover it with some kind of disposable plastic wrap? Every person would just throw the old cover away and new one would be automatically in it's place.
Edit: There's a condom joke in here somewhere....