expecting pins 4/5 to be pwr/grnd, is there an easy jumper I can do in the sled to make this work?

Even on the stock harness this is done externally from the sled - by splicing wires.
The stock harness is documented here and the functions of the various pins/plugs here.

The wires to pins 4, 5 and 8 on the serial plug are spliced and shrink tubed to the wires coming from the connector, fairly close to the connector. In the second pic on this page, you can see the splice on the ground wire (furthest right).

/Michael