The truck is a 2003. OS number: 15189044
As an update I ended up using the relay but hard wired the relay control to ignition switched power. I tried to use the DSP output but it would not sink enough current to switch the relay so I would have needed to install another relay/circuit. Works well though it is annoying to have the pump running when the ignition is powered and I'm doing an ECU flash and it would be nice to have the safety feature where the pump shuts off when the engine shuts off. Probably not as critical with diesel as with gasoline.
For anyone looking to do the same relay "reuse" you will need the fuse box pins to replace the existing ECU connection to the relay and will need to connect from the switched side to power the pump. The fuse box pins are Delphi Metri-Pack 280 series and the part number is: 12129061. I found them on Mouser part number 829-12129061. Ended up with a nice clean install. Once you pull the relay block you can get to all the pins and easily swap them around.
I also tried messing with the second tank values in EFI Live. I was never able to get the relay to switch on no matter what I set for tank sizes or fuel level calibrations. I suspect my OS does not have the second tank code enabled. Either way I gave up on that path.