You could draw out rectangles in EQ7, and see what it looks like.
Otherwise, the only way would be to add borders unevenly, e.g., one on the side and two or more wider borders on the bottom.
One more thought. Try printing out 2 copies of the picture in the pattern. Then try overlaying the pictures. The first thing I tried was to take the top row to the bottom, but then the red is next to red.
Then I tried pasting the 2d and 3rd row to the bottom. But then there is a partial purple next to purple. But if you change the original bottom right to orange and keep the whole partial purple -- take the copy, leave the orange in the upper right, the purple half in the top row, then cut out the rest of the top row, and paste that over the bottom row of the original. That will give you 2 diagonal rows of the optical illusion. The quilt will be 3x5 rows. PM me if this isn't clear.