Ive been doing it for a few years, at first I set it up with the AB line the same as the combine, with an offset, which worked perfectly.  Lately I've been lazy and just loading the AB line from the planter and shifting it to "here" when it's right.  For that to work I have to have 2 lines, depending if I'm going north or south, and I just click between them.  This way I can set the lines up as I'm working in the field, even while I'm driving unloading on the go - no setup time.  Since the planter tractor is the grain cart tractor, I have all the planter lines in the monitor already.