Hi Stefano, if you need a snap point to target the center of an object's bounding box you can create a point object there using the BoundingBoxCenter command:
http://moi3d.com/3.0/docs/moi_command_reference10.htm#boundingboxcenter

It could also be possible to make a plug-in that would move an object by it's bounding box center onto the bounding box center of another object, would that help?

- Michael