He shouldn't even have the power to "unmarry" people, nobody in the government should.
I don't see what the problem would be by having two separate recognitions of a partnership. The government should recognise civil unions only, religions should recognise marriages only.
If you want to be recognised as a couple by the government, have a civil union; if you want to be recognised as a couple by your church, have a civil union and get married. That's as easy as you like.
Then it's up to the churches themselves to say whether they recognise a homosexual marriage or not.
Ron Paul sounds like he has the right idea on this one.