I took some of your suggestions, and since I had a rather large strip left over that was already sewn together, I split the backing in half, inserted the strip across the middle, and voila - instant length :)
I was planning on quilting it on my machine, but I gave up because I simply couldn't get this massive thing pinned right, so I'm going to wait until my friend is finished with the king quilt she currently has on her long-arm and use that instead. Since I'm not doing a fancy design, it shouldn't take more than a day or so to finish using her machine. She's such a gem to allow me to use her machine - I just have to provide my own thread - she provides the machine and her expertise, along with great company. I'll definitely bring lunch when I go though :)