ok.. it turns out that I was just flat out wrong about how ERC works... so I think what I have is a separate rig for the boots where they conform mostly just to the hip.  From there all joint rotations are ERC slaved to the base figure.  The drawback is that this will likely make it more work for an end user to transfer morphs or scaling from the base figure to the boots, given that their actual body parts are technically not the same as dawns even though the groups will still match 'for the most part'