new spell states / extra spell slot weapons

I apologize if this is known, I ran some searches but didn't come up with anything.

Is there a good way to automatically add a new spell state to an empty slot in SPLSTATE.IDS? I think I'd like to use it for a couple new things I'm working on. (Here's a preview: what if you didn't lose your extra memorization slot from the Zerth Blade or the Mage Dagger, just because you switch away to a sling for a few seconds?)

I might just go ahead and squeeze this into extraprof20... but I'm up to bit6 in that stat, there's not much room left for more stuff.