I don't remember any such command, and having had a quick look through the source, I'm pretty sure it isn't there. Rotatebuilding yes, rotatetexmap... don't think so I'm afraid.
f
oh, you might want to try messing around with the direction you lay the startblock when you set the texmap. I think if you start it like going from north to south or something, it might make it upside down or flipped.