Diamond hot end plus support material extruder

Hello guys,
I have a bit of a challenge for you. I have purchased a diamond hot end, and I want to run it next to my original hotend so I can print colors with the diamond, and supports or ninjaflex with the original. I am running Repetier firmware.
I saw that there is a procedure in the reprap wiki for mixing nozzles in Repetier Host, but it doesn't look like I can specify a separate nozzle just for supports. Is there a way to do this? I know I can set the offsets and everything, but the tricky part is telling it which extruders share a hot end and which don't.
Thanks in advance!

Looks from the Repetier v0.92 configurator that the firmware only has a toggle for mixing extruder or no mixing extruder, with no provision for a hybrid configuration. RepRapFirmware is fully configurable for any configuration but only works on Duet or RADDS and your configuration would require a Duet and DueX4 expansion board.

That's pretty much what I thought. I will have to see if I can make it work then. Anyone have an idea of where I should start with editing the firmware?
I have an MKS Base V 1.2 board, and I was planning on using a CNC expansion board to add 4 more stepper drivers per the reprap wiki page. I will use the auxiliary pins on the board to assign to each stepper.