Hello Rustaurius.
I just finished this functionality on my site using your plugin as I needed so I could not wait an implementation :). I made it in order to be able to use another shortcode so is basically working like in your plugin style. I am using the version of the plugin 1.15 but I think it won’t be a big trouble to integrate it even in your last version 1.19 as is an extra file in the shortcode’s folder and a new function that needs to be added to a file “Process_Front_End_Forms.php” to be more exact. If you want a help on this one maybe you have a git of your project where I can download the latest working copy make this change..and send it back to you with instructions of what I changed.
Just let me know your email address, or just email me to [email protected] and i will reply there if you want to help on this functionality as it’s a quite important one for a registration plugin ??