Yeah, in hindsight it was obvious. That's what I get for doing this stuff at night.
I am not quite sure where you are going with your "N-1". Bureaucracy saves its incremented number in the metadata. You can set any number you want there or in the increment field itself, but I see no way to tie it to the numbering plugin or to anything else unless there was a way to directly write into the Bureaucracy metadata with that.
But honestly, this was just one of those instances where I am probably just a little too lawful stupid about things. Nobody is going to make a big issue about there being two different sets of identifiers in the same database, It just doesn't look as neat as I'd like. If I was working for a multi-billion dollar company, sure, I wouldn't do it. But as things are, I should have probably left it alone. I was just so annoyed that our autoincrement hack in the Struct plugin didn't work for the ordinary users without admin rights for the database. I am starting to ramble...
Thanks for all your help.