Took you long enough Jimmy
only joking!
I actually did a set of masks with my vinyl cutter and found that by only having one window mask and effectivley cutting both window and border as one you get perfect line up. (similar to layering I suppose)
You apply them as one with application tape, paint, then remove the outer and paint the border. If you are worried about creeping through the cut then you can cover with thin masking tape.
Works great but I don't know if you could do that with your style of mask?