Looking for Wisdom on Covenant Marriage Agreement

Dear fellow pastors:

I recently received a request to perform a wedding from a member of the congregation I serve. She's a widow who has recently met someone and they would like to get married. As she was talking to her attorney, he suggested to her that she enter a covenant marriage agreement. As the attorney explained it to her, this fulfills the couple's desire to make a commitment to each other before God and the church (but it explicitly is not a marriage for civil purposes). As I understand it, the result of a covenant marriage agreement is that there is no legal involvement by the state at all. The two would not be considered married by the state.

The main reason for doing this is that marriage would be very detrimental to them financially. It could bring substantially significant issues with regard to pensions, taxes, insurance and bequests. She's 77 years old, a devout Christian, and I have no doubt of her desire to do this the right way.  

What I can discover online is not particularly helpful. 3 states appear to have accepted (maybe even adopted?) covenant marriage agreement provisions. The standards for getting a divorce under them are more stringent—apparently a greater commitment than traditional marriage under the law. The blogs I can find only involve somewhat scary anti-government folk. Anybody out there have any experience/wisdom on the matter?