Griffin autopilot can be modified to fit iPhone 4 with bumpers
I love the Apple bumpers especially since it raises the phone off the surface enough to keep the glass fresh and scratch free.
You can remove the black cover from the end of the connector. It seems that the black cover is pretty much only held on the connector by the raised "Griffin" logo the protrudes through the cutout on the top of the cover. Take a knife and pry the cover (from the wire side) so it lifts above the logo and slide it off the end. Voila!
You will notice that the gray sleeve underneath now slides a little. It will get worse as you connect and disconnect your iDevice numerous times. To alleviate this I placed a small bead of crazy glue along one side of the connector where it touches the gray sleeve fully. (the other side has an indentation and only the very ends touch.) This effectively secured the sleeve to the connector and it has worked out great.
Hope it helps.