Portal2 is now supported, starting with the second release of THD (version 1.0.1.5).  Its on-screen control and gestures are more like that of Skyrim.  Use on-screen control to move, jump, and shoot.  Use pan-view to change the view.

Please check http://support-remote.splashtop.com/entries/21229872-thd-manual-instructions for instructions of THD.