Just in a physics standpoint, I think using handcuffs wouldn't be the best method for suspension by wrists as they are extremely thin, and would force body weight onto small parts of your wrist bone. My suggestion is probably to use a lot of rope wrapped around the wrist several times to increase the surface area of the point of contact.

Plus, I think there some wrist attachment that are soft that can be tied to ropes which make suspensions a lot less painful.