Work shift G54 G55 help

I have a Mori Seili NL2000 with a Sub spindle and Y axis...It is the 2008 model with Mitsubishi controls...I set the face of my part at G54 Z zero and after cut off the part is in the Sub spindle and I set the face of that part at G55 Z zero. I store these positions in the program using the G10 process...But I started thinking, since I face of the part and establish G54 Z zero, and I know the length of the part, I set B zero with the face of the collet to the face of the part...shouldn't there be a formula that could calculate G55? I remember pack when I ran Horizontal machines, we just needed to pick up the first side of the part on the tombstone and the calculations would follow the part no matter what angle we rotated the pallet to. I would think the CNC lathe would have something similar since the machine knows the travel of B (Sub Spindle) minus the part length plus the amount I chucked on, etc...It sounds logical in my head...but then so does Warp Drive on Star Trek, so what do I know? Any help is greatly appreciated! Oh and if we do get this working, I have to copy the process to a Eurotech B545SLY!