I noticed in the shiftpwm site, there is a "push-pull line driver" for running data lines a long distance.
http://www.elcojacobs.com/using-shiftpwm-to-control-rgb-leds-with-arduino/
Somehow I doubt that it has anything to do with shielded ethernet cable, those are a couple twisted pairs of wires with a wrapped shield and drain wire, its not very good shielding. Cable TV type cable has braided shield, that would work good if you really need shielding.