Make sure the camera end of the bellows is all the way back if you haven't already. Mine will fit but I have to gently "force" it due to clearance issues with the body. I plan to take a dremel to the bellows so that I don't stress the body with repeated uses.
Since you cannot move the camera on the rail due to its size the "dogbone" connection that joins the two rails serves no purpose. You can unscrew the two endcaps, remove the dogbone and then reinstall the endcaps. This will give the much needed extra clearance to allow the bellows to be mounted and then rotated into landscape mode with zero interference. If you have the battery grip you may want to grind a small bevel onto the tripod mount part of the bellows so that it doesn't interfere with the grip.
Works well enough for me, now I don't have to cringe whenever I mount up the bellows.