How might social conservatives be convinced to support gay marriage?

Rob Portman, a Republican Senator from Ohio, recently decided to openly support gay marriage after his son came out to him and his wife. What can be done to help other conservatives see gay marriage in a new light -- as a matter of liberty and individual identity?

See: http://www.dispatch.com/content/stories/editorials/2013/03/15/gay-couples-also-deserve-chance-to-get-married.html