As long as the state does not recognize "religious marriage" as a legal institution, so that the government classifes all legally-recognized marriages (same-sex and mixed-sex) as "civil marriages," I believe we have an acceptable result. If there is some persisting distinction that I haven't picked up on yet, then the result would still be icky. Legal consistency seems to be at the heart of civil rights, whether the legal relationship is titled "marriage," "civil union," "civil marriage," or "wally polly oomf."
Granted, many religions will deny same-sex couples the right to marry, but that is their own right, because it's within the context of the particular private institution rather than the public sphere. After all, it is common for religions to not recognize or to refuse marriages for reasons other than the sexes of the two people, even when people are legally joined or are permitted to join.