Crazy thought...
Could you convert the drawing into an Inventor *.dwg format (assuming it's not already), rotate the TB in ACAD, then use it in Inventor (converting it back into a *.idw if necessary).
I haven't tried it, and I'm not able to jump into Inventor right now (i'm typing this just before I have to go into a con call), so I could be way wrong.
But I just thought I'd throw it out there.