My RBW list (and etsy) friend TapeBubba modified his Rivendell/MKS Grip King pedals to have more lateral support. Watch the video and see how he does it.
I think it’s a great hack. I’ve had that ‘roll off the side of the pedal’ feeling myself, and my feet are fairly narrow.
He removes the cage pieces from the pedal, makes a U out of aluminum strap to go around the body of the pedal. The bottom of the U makes an outside edge for the pedal, and the cage pieces are screwed back on, sandwiching the strap in place.