Blend you fools!

The special sauce for blending a thumb joint in VR is to weight the joint from a Max of Float Array result, where the values in the array come from the absolute stickX, stickY or stickPressed captured values. This is super short and sweet.

So I'm done with the animblueprint for VR hands, and just need to polish up the poses. In UE4 an imported animation can be tweaked using a keyed animation offset curve, there's no need to go back and forth between UE4 and other animation software to correct the poses for the fingers.