one other thing I was going to mention about FAWM and 50/90, they do something called an exquisite corpse where multiple participants each take something others have previously worked on and they add to it and pass it along. It seems more structured (like a game) and maybe more restrictive than what you are thinking but might be interesting for you to check out (personally I do not care for these that much!) Here is a link to some conversation,

http://fiftyninety.fawmers.org/content/exquisite-corpse-charlie-delta-echo

and here is a link to an example,

http://fiftyninety.fawmers.org/song/1888