Programming a mec for basic functionality is trivial, even without the WPI library function.
Just take your driver commands for forward, strafe right, and rotate clockwise, and compute the speed of each wheel as follows:
Code:
front_left = forward + clockwise + right;
front_right = forward - clockwise - right;
rear_left = forward + clockwise - right;
rear_right = forward - clockwise + right;
... then normalize the wheel speeds as necessary before sending the commands to the motor controllers.