Anyway, I've stumbled across the following paper: Implementing Deletion in B+-Trees
It has an elegant recursive solution with pseudo code and flowcharts. May it aid others who need to implement B+ tree deletion.
... Or you could just use the Berkeley DB code without having to understand any of the B+ tree code at all.

I forgot to add: Not only was I glad to stumble across that, I was also glad to know that it wasn't just me that felt like there was a lot of handwaving going on with regards to how to delete from a B+ tree.