I think I'm leaning in Lucius's less tongue-in-cheek direction. For most strikes, a simple -1 for only using the dominant hand, -2 only to maneuvers that would normally use two (throws, for example). Perhaps a higher penalty if the off-hand is literally tied behind his back, due to the reduced range of body motion, or maybe not more OCV penalty, but a -1 to DCV. If he ties his *good* hand behind his back, -3 OCV makes sense, maybe with that same -1 DCV for actually tied.