My Solo2 showed up yesterday so I'm finally getting around to the wiring piece.
AFAICT, the short answer is, the Awron harness is just a big Y connector that the BMW female pin plugs into one side of, the Awron gauge plugs into the other, and then there's a female pin on the base of the Y (that needs a male pin to fit into the plug) that then plugs into the original BMW plug strip.
We need to replicate this, which means on the Solo2 side we need to solder together a Y (or use a tap on the Solo2 wire, e.g.
https://amzn.to/3EImv3Z*) for each wire, with (in the tap case) the Solo 2 wires getting the aforementioned "no part number" pin to go into 61138373583, and the tap getting one of the pins from 61132360043, which replicates the BMW pin and gets plugged into the original plug strip.
I'll gather some parts and test things out and write up a Solo2 specific install guide based on the knowledge from here.
* If we wanted to be fancy, a two wire tap like
https://amzn.to/3FHfdOZ might work even better, though I think the Solo2 uses 16 gauge wire so it might not fit :/