Twenty twelve : collapse mobile submenu items

The toggle menu button on twenty twelve mobile screens could use a way to collapse the sub-menu items like an accordian, so that the menu list does not look too long when the toggle is activated. I’d like to see some arrows on top level menu list items to toggle them down to reveal the subpages as needed. A question was asked about this in the thread of another post, and some jQuery code was suggested, but without a clear indication of how to use it and the o.p. was not able to get it to work. I think the jquery is over my head, I am hoping for step by step help. My guess is that many others would like to implement it if it were possible.