At least on the 737-200, and I suspect some later models, you would not want to select the generators on until you physically see the towbar being hauled away from the a/c. Remember that you will have the "A" hydraulic pumps (nose wheel steering) selected off. They are powered closed (off) and by momentarily interrupting their AC power source, you run the risk of powering the "A" system which could give the nose wheel, and anything attached to it, a nasty swing.
Our procedure was never touch anything until the bar was clear. There was no nosewheel steering bypass pin on the early 737s that I flew for 8,000 hours.