Is there any reason why you couldn't or shouldn't serge that first border on? Sew it and trim in one fell swoop? (As long as you pin the border carefully first without stretching it...)
I am getting ready to put on the borders on my first French Braid and I have a serger. Seems like it would do the trick, but wouldn't that leave a bulky seam in just that one line?
Dunno...