I made a king size quilt in a class once and the teacher told me to just rip the fabric. It was scary, but I just held my breath and did it. It worked fine, the only problem I had was the edge was not a perfect clean line to work with when sewing it to the quilt top.
I think I just nicked the fabric right beside the selvedge, then nicked it again the right distance from the first rip.
Of course I was not working with fabric that had a border type print, that would have to be perfectly on grain to work.
Good luck.