You can certainly use a True Blue pass to fly someone else. I just flew the bf back up from TPA b/c he finished his biz trip early. However, it is against the program rules to take cash in return for doing this. Many folks here get around this my trading what the two parties believe are equivalent points/miles in different programs. The only thing is you have to be a member for a certain amount of time before you can use Coupon Connection. See the link above.

It is worth pointing out that some argue that trading is a Grey area and may still violate program rules. So you should do this at your own risk.