What about a RelocationWiki as a tool to relocate Offtopic contributions (e.g. Spam) to a different place. Here the contributors have the chance to relocate it into another place, where it is possibly more welcome.

After a week or so the new entry into the RelocationWiki times out is automatically deleted. (garbage collection).

Other possible names for such a Wiki: GarbageCollectionWiki, OfftopicWiki, ThrashWiki, TrashWiki, you name it: