Hi Guillaume,
Apologies for the delay: my last response appears to have vanished into the ether. Let’s try again!
First of all, I should note that the amount of support we can offer for custom dev tasks like this one does tend to be limited, so we won’t be able to go into too much depth with this. Of course, I’ll be happy to point you in the right direction if I can.
Essentially, the trick would simply be to listen our for new submissions of the form. In our case, we do that during the wp_loaded action – perhaps that would work for you, too? If not or if you are still having difficulties, perhaps you could share a snippet of code illustrating how you’re handling this so far?
Thanks!