After searching and testing several hours without having succes I've to do it another way.
I'm looking for a formcheck, which can check and give a warning if there is a field missing, but can save the form even when user saves the form include the missing field.
Sounds strange, but it is a check for a 95% obligated field, but still has the possibility to save form while user knows he is missing a field.
See it as a warning, so like ' are you sure you don't want to fill in your prefences ' ?
If user clicks Yes, then save the form incl. the missing field.
If user clicks No, back to the form so he can fill in the missing field.
It's that possible? And where to find such a script ?