How can I begin paying child support when the mother doesn't want it?

I am currently paying child support for 1 child in Texas via the courts and would like to also establish a child support account for 1 child in Louisiana. I have been paying child support for the Louisiana child since birth (4 yrs) and there has never been a problem as the mother and I live together. I would like to set up a legal child support payment account with my Louisiana child as a safety net but the mother doesn't think it's necessary to establish a child support account since I've always supported this child since birth. I am listed as the father on the birth certificates. However, I think I should because if she and I one day decide to split, she will probably file for support and if no record is on file that I've always supported my son from birth, I will legally be considered never having supported my son and will be considered as 4 years behind in child support payments. Of course, she says she would never file for support but I'd rather have a legal record that I've always paid support for my son. How can I go about setting up an account without her knowledge?