Hi all,
Unfortunately this is not easily achieved and wouldn’t be possible now without hacking the core. But it’s too complicated to be able to provide a solution here so you would need to hire a developer if you needed this feature now.
It’s a great idea though and something you may want to request as a feature in an upcoming release. I know we’ve had other users request the ability to include additional fields in the form (which we don’t have the ability for now either) and this could be something that could go along with that functionality.
Sorry I cannot offer more here!
– Jonah