I thought about this some more (I really should be cleaning, but this is way more fun). You could add strips to the sides of your panel to make it square, then add triangles to each of the 4 sides to put it on the diagonal, like a square in square block:
http://www.equilters.com/library/PFP...in-square.html
Again, depending on your table placement in the room, and what the image is in the panel, you are looking at a one direction runner, but that might be OK.