If I'm understanding correctly, the BT-60 is just friction fit in there for now? If that is so, pull it out. Then grab a large dowel (1-2" Dia.), and wrap sand paper around it. Find the vertical center of each pentagonal panel, where the BT makes contact with them, and sand on that line. It should only take a little bit on each panel to relieve any stress.
That may work. I just want to be careful not to thin the pieces down too much, though, and compromise strength. Once I get the centering rings in there I'll get a better idea whether it is really too tight, and if so by how much. Once I try it I'll post back here; gotta go dig through my (somewhat limited) stock of centering rings.