I figure most people won't want to sacrifice easy dual extruder capability, and the connectors the Taz uses into the enclosure are quite expensive ($10-15 range, if I recall). So, I've decided to use a slightly modified stock 2nd extruder harness such that paste extruding can be connected out on the carriage just like any other fast-swap extruder. I'll follow up later if you want a special purpose cable just for past extruding.
According to the Lulzbot specifications, however, the 4 stepper control lines should be shielded. The cable I used to make that second extruder harness has two inner foil shields as well as copper conductor that runs the length. I added an additional connector onto that ground conductor and will use it for a ground on the secondary harness that will go to the paste extruder and it's enclusure. In addition to being unshielded, the wires on the paste extruder are a bit short for proper positioning, so I intend to splice those within the enclosure and switch to shielded.
What I don't know exactly is what sort of ground conductor is used in the stock cable shipped with the Lulzbot dual extruders (I didn't wait for the release). If anyone has one, I'd appreciate if you could peel the jacket back a bit and take a look. The only one calling for ground in the BOM is the one connecting to the stepper (red, white, green, and black, if I recall). If there is a suitable ground you could slap a connector on, it would eliminate ordering another pin and running a ground wire the entire length of the harness.
Please note: I didn't mess with the primary extruder harness due to future possibility of printing things like silicone with underlying support structures for spans.