Before I spend the money to buy a second nice damper pedal, I tried mapping my footswitch to the sustain controller to see how two pedals feels. (This wouldn't be an ideal solution because I'd have to edit every single program rather than make one global controller assignment.) I now realize that two pedals should be enough. I only need an extra one to the right because when standing and shifted right, it's difficult to pedal with the right foot because you need to cross your right leg over your left to reach the pedal. When shifted to the left, the pedal positioned over middle C is fine. Alternatively, perhaps I'll try learning to pedal with my left foot when shifted to the right. Since all my techniques are pretty basic, I would think I could bring my left foot up to speed quickly enough. Otherwise, a second pedal with stereo Y-cable looks like the way to go.
In either case, it looks like there's no way to keep continuous control over the sustain pedals when you reposition your body by shifting your feet left or right. Your feet lose contact with the floor when taking a step. I might try the pressure pad idea if I really want to keep continuous control over sustain by dragging one or both feet to the right or left.
keystring: Not clear what you mean: your suggestion looks like it's for playing sitting down (right?). But I only play standing, and my keyboard's too high up until I can find one of those specialized high chairs, which would give that "sitting while standing" feel. Perhaps that's what you meant.