Sounds like the legally smart thing to do is to lie when they ask you where you're going to work after you quit. Which sucks. It's not good to lie, and it's bad if legal circumstances effectively require you to lie, but I guess it may be necessary here.
A couple of suggestions for things you can tell them:
* you want to travel the world for a year and find yourself.
* you're going to start your own company. Maybe even register at the chamber of commerce and give them your card in case they want to hire you.
* you need to take care of a family member.
* you're burned out by this work and are going to work in retail or something.
* you've got the opportunity to turn your hobby into your work.
* you're going to move out of state/out of the country.
* it's none of their business. (Not a lie! But if they suck, it might make them suspicious and do some research.)