From "The Fender Bass: An Illustrated History":
"In 1960, Fender added the strap button to the back of the Jazz and Precision Headstocks. (Traditional players used this button to help strap the bass vertically, allowing them to play as they were accustomed in their transition from Upright to electric Bass)
If you try this method, I would really recomend strap locks, as the strap tends to slip off very easy in this position.
