I posted a video showing a workaround you can use to create spherical constraints. We are looking at the entire constraint workflow and plan some exciting improvements. (http://www.youtube.com/watch?v=0OCwFRCXBsc)
One detail, to get the work geometry into the components you should activate them by double clicking in the browser, or selecting "Activate" from the context menu. This part of the video may not be very clear. You can tell the active component in Fusion by the Blue background in the browser.