Route TCP responses (ACK) through another interface

view story

http://serverfault.com – For reasons I can't go into, I am working with a strange network configuration. I have a one-way higher speed wireless link, and a slower bi-directional wireless link. There is a network interface for each link (currently only UDP works on the one way link). My goal is to route all returning traffic (like TCP responses) from the one-way link over the bi-directional link. Is this possible? The network interfaces on both ends of the wireless links are currently on Linux based PCs. (HowTos)