Should it be ropes or nails? Thinking this through I can see why ropes alone can work. Simply place the knots where the nails would go (ankles and the carpal and ulnar nerve channel on wrists, never palms of hands!). There are two goals here; to extend the prisoners survival on the cross and try to equal the pain level of nails without loss of blood. The attached link demonstrates how this relatively bloodless crucifixion works. Crucifixions can be bloody as we all know but the key goal is death by slow asphyxiation. Here the prisoner crucified with the legs a bit up, in a bent position. He cannot lock and maintain position and take a full breath. Notice his gasping and the stretching of rib cage. This is the "dance of death", beautiful body movements and his moans and gasps provide the musical back drop. Of course he must be nude, as the bees, flies, and carrion must have full access before he dies. The crowds are allowed access to the prisoner for their enjoyment, but must not draw blood.
An excellent competition would be to rope up three, take bets on which one dies first. Or the executioners wager, that they can executed their prisoner without drawing a drop of blood. Now that is a challenge!