I don't think Masters programs would offer only science undergraduate courses. Perhaps you meant a post-baccalaureate program, where you earn no formal degree. Here's some information:
Boston University has a 2 year program that can be even done in one year if you go during the summer. A master's thesis is required. The program helps you do well on the MCAT as well. It offers advanced science courses.
MCP-Hahnemann also has a program, but I don't think it was geared to obtain a master's degree. It is to help improve your application to medical school as well as with MCAT. I recall this having more of the basic science courses you need to apply to medical school, such as physics, general chemistry, biology, etc. If I understand your post correctly, I think this is the program you would be most interested in.
Tulane Medical School has an anatomy certification program that prepares you for medical school by allowing you to take anatomy with their medical students. The program ranks your standing with their medical students, and supports your application to medical school with a letter of recommendation.
Finch (Chicago Medical School) has a master's program that allows you to take the first year of medical school with their first year students. If you pass, you are given advanced standing into their 2nd year class.