"Many schools will require you to take remediation courses if they do not feel you meet the course requirements for the graduate program. Some schools will allow you to take classes as a non-degree seeking student, which would provide both a way to prove yourself and also gauge the program and its suitability to you. I would check with the program to see how many credits they accept through this method though."
Correct. Also, many programs would let an individual in as a provisional student. You would take undergraduate courses in areas of perceived deficiency, however, they would not count towards your degree program of course so your degree would cost a little more than folks that took the necessary classes as part of an undergraduate CS program. Typically its no more than 3 to 5 classes from what I have seen on average. If you are good enough, you can also test out of prerequisites which is another way to demonstrate mastery.
Admissions tend to focus on both math (most will not let you in without at least 3 undergraduate credits of Calculus and 3 credits of Statistics) and computer science classes -due to the fact that many programs are aligned/attached with their respective engineering programs. Each school is a little different. A few that I found worthy of perusing: Arizona State University, University of Chicago -Urbana/Champaign, DePaul University.
Also since you mentioned MIT here is a snippet of their offerings and policies:
Current programs include:
Computation for Design and Optimization (CDO)
Computational and Systems Biology (CSB)
Medical Engineering and Medical Physics
Molecular and Cellular Neuroscience
Program in Polymer Science and Technology
The following interdepartmental programs are affiliated with the Engineering Systems Division (ESD):
eaders for Global Operations
Supply Chain Management (Center for Transportation and Logistics)
System Design and Management
Technology and Policy Program
Technology, Management, and Policy
Academic excellence is demonstrated by university grades, as calibrated by the Graduate Record Examinations (GRE) that establish a rough comparison between schools. The grades are examined in detail, giving preference to recent performance and subjects relevant to Technology and Policy.
For North American candidates, a minimum average of B plus is expected. This threshold may be different for other countries where the grading system is harder. For example, a B minus or C plus level from the major French Grandes Ecoles appears comparable. The faculty evaluates the record subjectively, recognizing the diversity of grading practices and personal experience.
Strong candidates for the program typically score in the top 10 percent of all three GRE areas (verbal, quantitative, and analytic writing).