Hi Michael,
Great to see someone else still using colorweb 250. I have 40sqm myself, its great.
Anyway, when I put it into capture I created flat surfaces from the Cube in the library and built the grid behind the pixels when in place to create the 'look' so I could light through it for the previz.
Depending on your design it quite fast. I created one vertical 5m long 0.01 deep and 25mm wide. Then lined it up behind the first row and cloned it with the Z offset to cover the 8m run. Same for the horizontal.
Hope that helps as a quick work around.
Jon