Shoe Rigging Questions

I've modeled some sandals for G3F/G8F, and have rigged them and saved as a figure/prop asset.  Although the sandals fit nicely, there is a lot of distortion when the toes are flexed, as seen in the first picture.  I'd really like to accomplish the "graceful sole-bend/toe dangle" effect as seen in the second picture, rather than the glued-on sandal look.  Way back, Victoria 3 had a set of morphing sandals which did this effect via adjusted bones in the sandals (V3 only had lFoot, lToe, rFoot, rToe rigging, which made it easier).  Looking at G3F though, there are no JCMs for the toe bend, as compared to the thigh bend.  My idea was to export the crumpled sandal, adjust and smooth it, and then re-import it back in as a morph to be driven by the toe bend.  Is this still possible to do without a proper or dedicated toe-bend JCM channel?

Thanks,

-David