The Secular Coalition for America (SCA) issued an action alert about this recently. They are trying to get an atheist to address the forum alongside the religious ministers. Lori Lipman Brown, director of SCA, is herself offering to attend the event on behalf of the secular community. I'm not sure that's the best approach, but for what it's worth, here is the link. And Lori is a good speaker, so perhaps she can go a long way to raise awareness.
It is certainly divisive to treat the non-religious (of whom there are far more than Jews or Muslims combined in the US) as if they do not matter. Furthermore, this is not a one-time event, if the organizer, a Pentecostal minister, gets her way:
"Daughtry has publicly stated that she hopes starting the Convention
with a religious service become a “hallmark” of the convention for
years to come."