First of all, keep in mind that you are doing PPC and not SEO. So, it will depend on the duration of your campaign. If it is for a short period, don't worry about it at all.
If you are having restless nights because of this, here are some ways: pick any one which you like:
1. Since the adCenter pages are in a different directory, disallow Google bots from visiting it by blocking them in your robots.txt.
These are the bots from Google:
Googlebot
Googlebot-Mobile
Googlebot-Image
Mediapartners-Google
Adsbot-Google
So what you want to do is, enter a couple of lines for each bot, like this:
User-agent: Googlebot
Disallow: your-adcenter-root-directory
where your-adcenter-root-directory is where you have the duplicate content.
OR
2. Disallow all user agents from accessing your adCenter directory/pages. This way, NO search engine will index your pages. Do this if you do not care about long term SEO for the adCenter pages. Your Adwords pages will still get indexed.
OR
3. Provide a backlink from adCenter pages to corresponding Adwords pages (should not be noticeable to users; somewhere down as part of your footer). This way, the Adwords pages will be treated as more important by Google. So they will almost never get hit.