In the intersection edit window, on the Green Bands tab, include an Action of 'Custom' that allows the user to manually (click, hold, drag) the start and/or stop green band limits directly on the Time Space Diagram (similiar to the way an intersection's offset can be adjusted).
I know the Action 'Start' allows the user to manually enter the Offset and Width, but I'll admit to being lazy and prefer the point and click functionality. This will allow the user to massage the green band, taking into account consistent 'gap-out' intersections and develop a more realistic green band without the back-and-forth use of the intersection edit window.