All are good suggestions, only an addition to Rumpin.
You of course don't want every encounter to nix it, but you should mix full/partial/none useful encounters.
Yes, it's a great trick, but there should be times when it flat out doesn't work. That's part of being smart with a build, is not relying on a 'one trick pony'. If you do, you will never enjoy the game.
Don't feel like you need to play into a one-trick, be real, and if it is a one-trick he'll eventually realize being really uber awesome at one thing simply doesn't work.
Then again, he may not be a one-trick. In either case, follow the full/partial/none if you can for all groups/encounters. It mixes things up, makes them continue to evolve, and focuses towards rounded characters/styles.