Okay, I lied, I tried it again.
For anyone who is having as much trouble as I had with Bellum/Linebeck - spin attacks are very good at getting him to the weakened 'Rub!' stage. Even when he's doing the cyclone whirlything attack, if you can manage to get your spin attack to go off (which for me isn't easy) and intersect him, it'll knock him straight to Rub. This is actually EASIER, for me, than dodging the blow while hitting him normally.