I have said for a long time that an employee should be able to extend their workplace benefits to their kids and one other adult - be it a domestic partner, a spouse, an elderly parent, etc.  The definition of "family member' is changing.  How many single people care for an elderly parent in their own home?  Are they not family?  if I want to pay the cost of insuring someone other than myself, then why not?
Then this is not a gay versus married issue - it would "generic-cise" it.