Pass form values to UM Registration Form

can you put me on the right path to passing form values to your registration page. basically I have a simple form with 4 inputs. 3 which I want to pass to the registration form. I have tried naming the form values the same meta name as the um registration form and also have added both forms to the same page but to no avail. I was able to integrate a confirm email element using your documentation but am not seeing anywhere that I can accomplish this task. please advise.