My suggestion would be to process each separately, save, and then do a Dynamic Align of the two finished images saving both as noted being aligned. At that point you can combine them using the LRGBCombination process by opening both aligned images, leave only the L box and choose that image. Drag the triangle over to the RGB image and save the resulting image. Note there will be a need to crop the image as I'm sure the dSLR image will be quite larger so the luminance data will only cover parts of the rgb data.
