Oh? Maybe it's just that the documentation specifically mentions ssh -L but not ssh -R. Can you do something like run spiped on a machine behind NAT or on a dynamic ip address to create a reverse tunnel via a publicly reachable host?
Well, spiped lets you say "when connections arrive here, encrypt/decrypt them and send them over there". But if "over there" is behind a NAT, there's no way to do that; you would need a persistent connection, which is what ssh does and what spiped is designed to avoid.
