Just wanted to send an update to all who gave me suggestions before.
I wound up repairing my broken b-pillar with 3d printed parts that someone had already made on thingiverse.
Using this thing, a Dremel, and some plastic bonding epoxy, I restored my b-pillar to good as new condition.
Here's the thingiverse link:
https://www.thingiverse.com/thing:2233260
Used the Dremel to file down the broken plastic, and epoxied the new part in its place.