I feel your pain. There are some pretty essential features that Adcenter is still missing. A MUCH larger negative keyword capability and value/ecommerce value tracking.
You're best bet is to tag all your adcenter destination URLs using this:
http://www.google.com/support/googleanalytics/bin/answer.py?hl=en&answer=55578
You can pass your keywords into the campaign term field yourself automatically. It;s what we do and works pretty well. Give me a shout if you need any help.
Managing Director
Redfly Internet Marketing Ltd