Hello Scott,
Unfortunately, rotating the bounding box of the reconstruction volume is not currently supported by PhotoScan.
The purpose of manual volume selection is to specify approximate region that should be processed during reconstruction. Usually it is not required to specify it very precisely, just make sure that the area of interest is inside.
Thus rotating the bounding box seems not so important in most cases. Nevertheless, in some cases it may be useful, so we will consider implementing this option.
With best regards,
Dmitry Semyonov
AgiSoft LLC