Before I got my LA when I was using a DSM on a frame (short-arm), I would turn the quilt to do continuous borders. If you baste the side edges of your quilt as you go down the quilt, you shouldn't have much trouble with extra fullness in the borders unless you've got a really wide border. If you're nervous about that, you can always pin-baste the borders before you take it off the frame or baste within the borders.