I've only seen someone pull the horse's head to the outside in the beginning of training the lope. What I've assumed it was for was, when you pull to the outside, it puts the hip slightly in. Making it easier to pick up the lead. I would NOT do this after the first couple times of working at the lope as it will encourage the horse to drop into the lead.
Its far more productive to teach the horse to move its hip over with the leg so that you can tip the nose in and pick up the shoulder.
There are no "tricks" to pick up the proper lead...only good training will make a horse consistant in its lead departures.