How to set pivot points automatically in sprite editor?

I have a sprite sheet to slice using grid mode. I'm willing to set the same custom pivot point for each tile instead of the already available ones such as 'center' or 'top left.' How would I go about doing this automatically? I don't want to have to set it manually for each slice. And I don't want to use other strange gimmicks involving increasing the size of my sprite sheet. Thanks.