The FB processor is also inclined slightly supposedly so you can watch the development in the first tray. You can see one of them in this photo:

http://www.flickr.com/photos/65271786@N00/5209751985/

There's a special clip also as Stan mentions above. But I've read here a few times of people processing fibre in the regular processors, I think by using two or three clips to support the extra weight of the fibre paper.