Awwwe yes the old Benelli finger. I have the same problem with my SBEII and my Dad with his SBE. I bought a little thing from the drug store design to go on a toe (for hammer toe or something). I cut the end off and put it on the middle finger and it seems to cushion it nicely.
My whole hand was black and blue after a day of shooting Cans. on lake St. Clair in Canada last year. This has solved the problem.