I'm sure I've seen a few mods floating around BCFiles that claim to get NFX 2 working in SP, but I can't remember off the top of my head. Try running a search there for NanoFX or Single Player.
As for making the game more stable...well even though NFX 2 is the root of many of BC's current instabilities, at the end of the day it all comes down to BC's outdated engine and the extreme memory leaks, which to fix permanently would require game engine modifications, which is currently not possible (and more likely than not won't ever be, unfortunately).
The CG Sovereign issues have more likely than not been addressed, if you're having the issues I think you're having. Check one of the FAQ's around here.