Even if you "removed" the hood, you would end up with a circular image with the top and bottom truncated. To get a fully circular image inside a film frame, you need to go for an 8mm fisheye (Nikon AiS 8mm/2.8 or Sigma AF 8mm/4).
If you want a "full frame" fisheye for your F5 you need to look at the 16mm fisheyes. They work fine on the DX formal as well, with the 1.5 crop factor the result is not quite as "fishy", but you can still obtain great results.