When lighting Hanukkah candles in the synagogue, we say a beracha "asher kidshanu b'mitzvotav.." on a minhag. Unlike kiddush in shul, and early counting of the omer in shul, nobody would say that one actually fulfills his obligation to light by doing so in shul (unless the person in question sleeps in the shul that night).
Are there other examples of saying this beracha on fulfilling a minhag?