They're working on it.
In the not too distant future, as we evolve nearer towards ‘synergistic convergence’, it's going to come close...
"I am greatly pleased when I see the Church, in its members, if not yet in its hierarchy, coming to recognise that there is no good reason to deprive same-sex couples of access to civil marriage. However, I think it is far from obvious how we, as Church, should celebrate these acts of union liturgically: whether in a rite that is similar or analogous to that for the sacrament of matrimony, or with something rather different. And I don’t think it will be obvious for some time." - Fr. James Alison
Photo: James Alison, Robert Pierson, OSB, Michael Bayly at St. John's Abbey, Collegeville, MN