Take the GRE Mathematics and Computer Science subject tests, and ace them (finish among the top 5-10% of all test takers).
Hone your software development chops.
Look at the web pages of some classes in CS systems, and turn the class projects into your “hobby projects”/mini-research projects. Publish some research papers from those mini-research projects at good conferences.
Put your portfolio of software projects on a repository, such as Gitorious.
Apply for grad school.
P/S: There are MS programs in computing/IT for non-CS graduates. However, there are usually too watered down that many employees don’t care about them, unless they are hiring for semi-technical roles such as product management, software quality assurance (or software testing), software build automation, and user interface/experience design.