I actually think you can do it with other sbi members too. Just need to discuss a price. Then you send a memo to the steembasicincome steem account saying "transfer all sbi units to xyz", it gets manually checked and then transferred over. Then whoever you sold your sbi units too transfers the steem.

If you don't get the steem transferred from that buyer then you just bring it up with steembasicincome and they will transfer the units back.