Here's an ICE 2 Bone IK chain with UV support that I've been working on for a while. I think I've got it stable now (no weird flipping). If you've got ideas to maybe optimize or expand this, I'd love to hear it.

I'll try to make a video sometime, but in the meantime hopefully you can follow my screenshot. First I create 4 nulls and 2 implicit bones. 2 of the nulls are the root and effector controllers, 1 of the nulls is the Up Vector controller, and 1 of the nulls is for the ICE rig. I had problems with reference names, that's why you see the same name in the screenshot. Make sure to update both names with your own names. To calculate the bone lengths, I first create a temp 2 bone chain (Animate/Create/Skeleton/Draw 2D Chain) and get the lengths from that. Occasionally ICE fails to update the bone lengths of the implicit bones. To set the correct length, temporarily Show Values between Get Rig.L_Thigh_Length and self.length. Seems to fix it for me.

Let me know what you think!
-Dave

Thanks for that...
I am, however, quite possibly (or rather: probably!) missing something obvious here,
but why would a bone need UV support?

Upvector, as in elbow/knee roll.

Oops, wrong "UV"

I was thinking the same thing when I first read the title, maybe it should be changed to "Up Vector" instead to avoid further confusion.

How do you name, for example, your Right leg's up vector controller?

Anyone gotten a chance to try it out? Any ideas how to organize the Reference name stuff better?