I'd suggest making the border and then making the braid to fit inside, since that is much easier to size.
I would think a row of solid, then a row of different colored blocks, and another row of solid will give you a line of twister down the the middle. You may have to unsew the pieces and resew them at the corners, and possibly cutting a few more sections seperatly to get that to work. Or you could do two rows of color to get a wider border. I have the mini twister and it gives a pretty small block after you cut and resew.
It really sounds like a neat way to make a border.