In the source code there is this USEXPSTORAGE compile option.
From what I can see from the source code, it enables a XP backup system which as far as I can see, allows for XP backup for up to 5 minutes.
Drawbacks: It uses the same IP system as the builtin IP banning system.
I found only one thread about this topic: http://www.splashdamage.com/index.php?name=pnPHPbb2&file=viewtopic&t=7290
Has anybody had more experience with it?