3
As Richard explained, it is easy to do, however, this is not recommended, because you make it easier for spammer bots to register.
Our recommendation is to have both forms, and save it only after the Advanced form is filled out. This way when the bot comes and fills out the first form, it clicks on the "Submit" button thinking that it is now registered and leaves. But since the data is not saved yet (because it didn't fill out the Advanced form), then it doesn't register and you have one spammer registration less...