Open up civil partnerships to opposite-sex couples, and then repeal divorce for future married couples, (not existing ones), once your Judicial Separation legislation is fully up to speed with your existing divorce provisions.
Judical Separation does everything that divorce does, except dissolve the marriage.
This way there would be traditional, indissoluble civil marriage alongside dissoluble civil partnerships, and couples could have a choice between the two – or between those and just living together informally.
This idea is important as a way of restoring traditional, original, indissoluble civil marriage which could prove exceedingly popular amoungst couples intending to spend the rest of their lives together.