Looks like you can target the user agent:

"Google Chrome Frame reports that it is available by extending the host's User-Agent header to add the string chromeframe. You can use server-side detection to look for this token and determine whether Google Chrome Frame can be used for a page. If Google Chrome Frame is present, you can insert the required meta tag; if not, you can redirect users to a page that explains how to install Google Chrome Frame."

http://code.google.com/chrome/chromeframe/developers_guide.h...