I have used the following wedding blessing prayer at the reception of a civil wedding. So long as it is kept completely separate to the ceremony, it can be used in this way, or indeed on any wedding occasion.
May the God of love surround you;
May the God of peace be within;
May the God of joy inspire your days;
And may you grow in love, peace and joy
As you share this journey.
As your love grows
May you know the love, peace and joy of God
Upholding and sustaining you
This day and for always,