I am not an image editing expert and this explanation will probably reflect that. I downloaded a high resolution image of the cover, opened it in Paint.net, and resized it to 8.5 x 11. I created a second canvas that was the exact size required by Lulu (~17 x 11) and, using the dropper tool to get the exact same colour, painted that canvas red. Then I copied the cover image over onto the right side of the second canvas and exported it as a pdf. It definitely took me a few tries to get exactly right.