you can pursue an informal post bacc at any school. You simply take classes as a non-degree student and then apply to d-school. I did that and was accepted into 2 dental schools. It was easier and less procedural to do it on my own, the only difficult part was that I had to find profs and develop relationships with them in order to get LORs. Most formal post bac programs have a committee that can write one letter thats necessary for admission