I am speaking from the perspective of a student in a 8 year BS/MD program.
First of all, are you talking about 6 years in total? or 6 years from when you transfer from JC as a sophomore or junior to the 4 year college?
As far as I know, this is pretty much impossible unless your JC has a built in program with the 4 year college and med school. I know of only one 6 year BS/MD program that is still in existence and know for sure that they will not take anybody except straight from HS. For programs that are longer, you will have to transfer into the 4 year college with the program, and show at least 3 semesters of strong coursework at that school before you have any reasonable chance of being accepted. At least thats how it works at mine.