as far as i know, there is no possibility to use any motion study from SolidWorks in composer
depending on what you want to achieve, you may give SOLIDWORKS Visualize Prof. a try. Visualize is able to import the appearances as well as lighting and the motion timeline with all keys included. Visualize has really great rendering capabilities, and delivers great animation videos. But there is not possibility to integrate text, ballons, arrows ore other actors. Therefor you are able to create stunning and realistic renderings! You may have a look at the Viz forum here.
As of now this is not possible but that's something we (Composer users) have been asking Solidworks Composer team for a long time. Hopefully we will get this option in near future.
By looking at the previous enhancements in composer i can say the development team is working hard to make the composer even better.
Have a nice day!