Does anyone know of a list of faiths, sects, denominations, congregations, etc. that welcome same-sex and/or plural marriages? I think such a list could help make the case that this is in fact an issue of religious freedom.
In the case of plural marriage, I think it would be a reasonable restriction to require the consent of all current spouses for someone to marry another. Maybe require all current spouses to sign the license. (Would other witnesses be required? I'm inclined to say yes, but I suppose all the licensing details would be left to the states.)
Follow up: It would be tempting to try to get an endorsement for this from Clint Eastwood, since with his support for same-sex marriage and work in Paint Your Wagon he'd be a natural, but in light of recent events I think he's a bit too risky.