I guess maybe if you tried to share a ground wire, you could use a component balun and splice the 232 onto the extra wires. Biggest issue is you aren't going to find a device that likely does that over a single cat 5, unless they are multiplexing the signal somehow, and then I can't wrap my head around why the time/money would be wasted on the R&D when you could use those extra two pins (not being used for component) for something solid.