I think the Clubmans stack a few washers under the end of the big washer. This accommodates the length of the rubber so it doesnt press on the shifter bushing.
They have manually cut a hole in their rubber - it is rough - so you just need to cut the hole in the end of the pillion rubber, and then shim the stack so it is correct.
Now, the pillion rubber has flared ends along its length. With other rubber bits I have taken a Dremel with a sanding drum, and used that to sand down along the circumference with excellent results. You could do that as well.