Pretty sure that most (if not all?) RN-BSN programs require the "RN" half of the equation to get started. However, if you know where you want to complete your degree, you can discuss your goals with them and find out what's required as far as non-nursing courses, and at least get started on those. The danger with that is that sometimes curricula/requirements may change, and you may find you need more credits or have taken some classes no longer required.
In any case, let us know if you find a program that will allow you to start without the RN. Good luck!