Excuse me? Now, marriage is not a religious institution? I thought one of the main arguments made loudly by the gay community is that the traditional definition of marriage has no secular basis. That's a switch.
I think my suggestion enhances the government's role as preserver as oppose to destroyer. In fact, my suggestion would even accomodate polygamists. So, a Mormon or a Muslim would be free to have several wives and it's none of the government's business. But your marriage would come under your church's jurisdiction.