Give any two people who desire to live in an alternative to traditional marriage equality before the law. Have two forms, a traditional Marriage License and a Covenant Couple License (or satisfactory other name). Any law affecting marriage, family, tax benefits, etc. would be applicable to both. The two licenses could probably be filed under the same heading.
This keeps the historical interpretation of the word marriage intact and yet allows for the rights of those with a different need. It allows for a celebration of either event.