Your idea of seeding some /dev/random or attaching some /dev/random to emails sounds like a great idea, and also funny, to me. We should definitely do that!
Then spread the word and give them something to spy on.
I say we go for it.
Alternatively, we could set up a mesh of dropbox/cloud accounts. People would connect in pairs and generate their own huge files of garbage. Then they would copy it into each of their dropbox directories and it would propagate n times. If everyone does this every day (write a script to generate random data), there will be a continuous stream of randomly encrypted files across the network. When your cloud drive fills up, delete older files.