What if you pay the network to host your blocks by hosting some other blocks from the cloud, at some m:n ratio? The cloud (some random peer) could periodically check your block inventory and make sure you were still holding up your end.
Really, this whole concept is similar to torrents. Either ratio-based (upload at least X % of what you download), or HnR based (don't download something and refuse to seed it.)
edit: surely that's been done before?