No, it's completely blocked in by part B!
I've given up - I don't think the lock will be used anyway; I'm sure someone could get into the case if there really wanted to.
Instead, in an effort to reline and foam as much as the inside of the case as possible, I've foamed over the lock mechanism.
The case is 100% snug and safe for my three basses now (I'll update with a pic when the glue is dry!)