Hello Chirstian,

It can be possible by customization in existing code. You customise the code in below mentioned file path.
root/plugins/payplansregistration/auto/auto/tmpl/registration.php

if you require us to perform the customization for you, you can send request for a quote from us at https://crm.stackideas.com and select "Customizations" . Our sales person would be glad to send you a quote for the customization that you have requested.

Let me know if you have any query.