I've seen that used with a good rope halter with good results. They would take a lead or rope of any sort, but with a safety snap on the halter end and tie to the saddle. It does help with flexion, BUT done wrong could do MUCH more harm than good. I would suggest doing this ONLY if you are VERY confident with your ground/ longing skills and IF the horse is properly prepared for this. It can be VERY dangerous to the horse and handler both if done improperly.
Along the same line as "tying around", I would use sidereins with elastic and adjust them shorter on the inside with the horse well started and working on the bit already.
Good luck! I would assume with you asking here that perhaps it would be best to suggest that you work closely with a trainer.