Caveat: That the author has not seen this suggestion made certainly does not imply it hasn't been made; education about such a previous proposal is certainly welcome.
Any informed person has seen the arguments for and against same sex marriage. Recently, President Obama has publicly stated his "conflicted" position. That is to say, he completely believes that same sex couples should be accorded all the legal rights due those in opposite sex marriages, yet he is troubled with the idea of same sex partners committing themselves to a "marriage". Vice President Biden is on record stating that same sex marriages is "an inevitability."
Straights will say, "Why are you [homosexuals] pushing into our sanctified turf of marriage when you can have the same rights we do?"
Homosexuals will say, "We won't be fully accepted until we can marry."
I say there is a different approach.
My thought centers on the background for the institution of marriage.
Specifically, marriage is a social arrangment that is secularly sanctioned and temporally blessed. Clearly, a union of some sort has benefits to a society as a whole, but being married also entitles the man and woman to a kind of spiritual/religious moral entitlement while a civil union provides only parity that is codified in the pages of a dry and crusty legal text.
Now, for straights who are of a nature that does not ascribe to a particular religious point of view, they can be married by a justice of the peace or other legal person so appointed with said power. Thus, straights have the ability to take either track, religious or secular.
Homosexuals, without marriage, are entitled to only the secular route.
Conservatives, particulary those of a specially religious nature (they are often one and the same), will argue that our country is a secular society, governed by laws and not religious texts. (Herein lie the recent arguments about how our society should accomodate those whose moral viewpoint is shaped by religions: i.e., it is ok to beat one's wife because one's religions provides for it.)
However, what these supposedly secular proponents are really saying is, "We approve of secularism so long as it stems from the roots of a religious system to which we ascribe."
Therefore, I say let's completely separate marriage and civil unions. Churches can do marriages and the law can provide only legal civil unions. In this way, straights who oppose the religious schemata of marriage can have the civil union. Straights who wnat a marriage can have the church unite them in such but they must also have the civil union if they want legal rights associated with such a pairing. Homosexuals can have the civil union and, if their church approves, also have the marriage.
Instead of trying to force a square peg into a round hole (or vice versa as some say), let's separate the pegs and holes.