Assign color mode to pages in eDoc Builder (4/1, 4/4)

Currently we offer a product that's a 4/1 design online postcard and we want them to be able to upload their logo on the back. The proof shows in full color when it really will be black and white. It would be extremely helpful if you can assign each page on the eDoc Builder a color mode. Ex Page 1 would be CMYK, page 2 would be either CMYK or Convert to Grayscale.