I have known several engineers with a BS in Math that did MS in ME. I am not sure why automotive would be more restrictive. Most masters programs if they differ from your undergrad degree will require you to take make up courses in the subject area before taking the graduate level classes.
I would suggest that you go to your school of chose and meet with the guidance counselor. I would expect that they suggest taking classes to bridge the gap in your education.
If you are targeting the automotive industry, I am sure there is a reason for your passion. That needs to show on your application. If you are into cars and like working on cars by doing maintenance or restoring them, that can help on your application.
Apply for a job that uses your degree in an automotive company. If you work for an automotive company, it should improve your viability as a candidate.