iWork '09 Keeps asking to be Registered
I found this via google Disable iWork registration nag screen. 

defaults write /Library/Preferences/com.apple.iWork09 RegistrationHasBeenSent true


I have no idea if this will work for you. I wanted to point this out in case you hadn't tried it.

This blog was the first result in google from searching for iwork disable reg. If it doesn't work, you might see if there are more results that might help or a slightly different search that might provide something meaningful. In any event, good luck. I hope it helps.