The following is a block diagram of ClutterBox2dmm. It’s at a high level of abstraction, so most of the detail is lost. What’s of interest is that Cluttermm is stacked on top of Clutter and that there exists a Clutter-Box2d.
I’ve just extended both Clutter-box2d and Clutter-box2dmm to support the IsFixedRotation() functionality in Box2d. This hack isn’t hard. It does require modifying the C library Clutter-Box2d and then modifginy the C++ library Clutter-Box2dmm on top of this. The relevent commits are here and here. If you need this feature in Clutter-box2dmm you currently have to compile from source. Get it whilst it’s hot.