There appear to be two DOCMD IDs that would let shape designers rotate shapes 90 degrees right or left via Actions or double-click Events:
VisUICmds.visCmdObjectRotate90 = 1056
VisUICmds.visCmdRotate90Clockwise = 1494
The second entry, however, doesn't seem to work. It appears that DOCMD(1494) does not work--it's broken!