I guess that method would work more for people who are more close minded, they'll slowly move their viewpoint as you say things that very slightly disagree with their view, homophobia isn't a two-sided deal. While you are either homophobic or not, there are many many degrees of homophobia.
When I meant agreeing I meant either being silent when they speak negatively about gays or saying something similar that could quickly change the topic, and sometimes saying something that isn't directly opposed but otherwise could shift their view as you're friendly with them. Basically the total sum of it is to be friendly to them and to get rid of any possibility of being perceived as a hostile attack on their beliefs, which is much harder for people that are close minded.