You can sew two borders together and apply them without mitering the corners. I did it on a quilt I was working on just before Christmas and it worked out very well. It took a bit of thinking about how to do it, but once I had that done I liked the method and will use it again. I figured out the length I would need for both borders and the order in which I would usually apply them if doing them one at a time. I starched the fabric well and sewed the borders together leaving the seam open at either end so that I could attach them to the quilt without having to mitre them. I think I did the side seam first but I can't recall. Once you have the double border sewn on you just finish off the seams at the corners so that the inner border goes all around the quilt like it normally would. It worked fine and saved a lot of time. As you can see, adding the borders isn't my favorite job to do either! (I cut my borders a little longer than needed just in case, but measured and marked them carefully so that I would know the right length. The next time I won't leave myself very much extra fabric because it really did work quite nicely!)