i've been hesitant on replying to this, because i can see see more potential in it than simply archiving a current state of the LBK. as gpowless said, there could be something in this that could be used for versioning. i've been trying to formulate a way forward for this for a while.
but with regard to your archiving issue: are you using plotmaker 2 or 3? (your archiCAD version and machine specs could be quite helpful in your signature there . . .)
with the plotmaker 3 layout book file, there is the option to save your plotmaker data cache into a folder, (see attached screenshot). if you backup this folder with your layout book (LBK), this may be a way of achieving what you're after.
b e n f r o s t
b f [a t ] p l a n b a r c h i t e c t u r e [d o t] n z
archicad | sketchup! | coffeecup