Marriage, like baptism or communion is a sacrament of the church. The state can not sanction marriage in any way shape or form. The state exists to handle the paperwork and aspects of the legal union that results from marriage. If people wish to enjoy those legal rights, then the state, under the equal protection of the constitution, must grant those rights to people who wish them outside of the sacrament of marriage.
Basically, from a legal stand point, the state has no business being involved in marriage. If the church refuses to perform gay marriage, so what. Since the state can't baptize me, why should they be able to marry me. All unions, gay or straight should be civil from the states standpoint. There should be some basic limitations ( 2 willing of age people, no sheep... that sort of stuff) but after that the state has no interest. The church can dictate the particulars of marriage all it wants, as it is a sacrament.
DL;DR? Ban all marriage.