I'm inclined to say yes, by using multi-sig addresses (not very popular, they're a new feature -- a few months old or so -- in the official client). I'm foggy on the specific details of how they work, but basically it's like escrow except you can fuck somebody over. You need two keys to get at the bitcoins, each person has one key. If they don't agree, the coins sit there at the third address forever and nobody gets them.So you can get fucked over by some childish jerk, or ripped off by somebody who just bails if the scam doesn't work instead of giving you the coins. Something like that. But just the address you would use as the third in a multi-sig configuration, for another multi-sig. Then do it AGAIN with that one, and all of a sudden you have several people and you need the keys of all of them (all? I think all...) to get at the coins.Like I say, I'm foggy on the details so that may not work. I think it may be the closest you're gonna get though.