Joomla data user fields import to mijoshop opencart

I am using mijoshop which is opencart in Joomla. All my users must register through joomla to gain access (ajax register extension) and not opencart which seems to create issues with all the users as no one ever refills in the data on checkout as i guess they all assume the data is already filled in. I want a simple script that i can run either automatically daily (not sure if there is any issues with this) or that i click and run when i approve the users that will import the data from joomla into opencart. Obviously it CANNOT overright anything if it is already filled in by customer in mijoshop but all those that are blank fill it in. It must be tested by yourself and proven to be free of conflicts and support any bugs.