You are most definitely going to need to do some sort of academic program. Informal/formal post-baccs will only add to your undergraduate GPA, so even if you do really well and get a 4.0 it will NOT significantly raise your overall GPA. If you enroll in a graduate program, AADSAS will create a new graduate GPA for you. I personally would enroll in a M.S. program in a science-related field (preferably an SMP), as this was advised to me by several adcoms (but apparently there are schools that would consider a post-bacc adequate). If you want more info on these programs, search the post-bacc forum and also contact the schools you are interested in and get their opinion.