Pennyswings - you can obviously piece the backing if you like, to give you extra room to work, or, you can use John Flynn's technique of cutting the fabric on the diagonal, sliding the two sections to provide a wider piece of fabric then restitching. I've used his technique and have also altered it slightly by adding a diagonal piece of extra fabric between the two sections. You can see his instructions on his website at:
http://www.flynnquilt.com/workshop/FreeLessons/
The slice of fabric sewn into the back on the diagonal really adds punch to that side without much work.