Ok you can do something along this lines
Body rollingPlatform = BodyFactory.CreateCircle(world, 1f, 1f);
rollingPlatform.Position = new Vector2(0f, -36f);
rollingPlatform.BodyType = BodyType.Kinematic;
rollingPlatform.AngularVelocity = 0.1f * 3.4f;
rollingPlatform.SleepingAllowed = false;
rollingPlatform.Friction = 10f;
Body s = BodyFactory.CreateRectangle(world, 10f, 2f,1f);
s.BodyType = BodyType.Dynamic;
WeldJoint jp = new WeldJoint(s, rollingPlatform,new Vector2(2.5f, 0.5f), new Vector2(0.5f, 0.5f));
So in general you create a kinematic body which will do a fixed rotation then weld the platform to it at the position you want to and i think you get what you wanted.
I am sure there's a better way of doing this ,and it probably involves a fixed revolution joint ,but well .
Hope this helps .