Not on MKVI to my knowledge. It's usually easier to use foamcore or packaging cardboard for this step on these types of helmets. Cut out the shapes, glue down, resin over. This particular technique that you're trying typically gets used for the lines on the ODST helmets.
But good luck on this one, I'd suggest using vaseline or some other type of mold release on the foam so that the bondo doesn't penetrate the air cells and make your life miserable.