The “Control Bone” “CTRL_footRoll” shall during its rotation to the front toes set the “Influence” of the “Copy Location Constraint” on “CTRL_toeC” set to “0” so that this bone stays on the ground instead of moving slightly upwards (see video from 11:59 on):


When rolling “CTRL_footRoll” backwards the “Influence” of that shall be reset to “1” again in order to make the “CTRL_toeC move upwards.
The rig is here.