menu_addblank(menu, 1) and menu_addblank2(menu) did the same thing ("a" and "b" are at 6 and 7) for me and never shifted the exit button (the exit button stayed at 0).
menu_addblank(menu, 0) puts "a" and "b" at 5 and 6 but does shift the exit button to 9.
I could not get it to shift the exit button to 11.