Hi,
Great work ! I'll be in for 1 of what ever you come up with. I'd go for using the vacant switches giving the options of the existing auto, 15/85, 30/70, 50/50. Nice and simple.

I tried my JDM out in the snow a couple of weeks ago and can testify to the understeer. Overall, if I had the choice, I'd go for an ordinary old 4WD and a big toe on the brake where necessary.

Cheers........