There is now way to change it at the moment, I have a , little work around.
Create a new ArchiCAD file, hotlink in your original project.
In the new file you can rotate the building so it is rotated at the right angle.
By creating at hotlink you can have the changes reflected as you work, simply by updating it. This method works well for saving out DWG's as well.
I know ín your case you will need to have two instances of ArchiCAD running, but as I said it's a work around
HTH.
Cheers.
Ben