From Adwords Team: In line with our existing policy, we will continue to require that your ad's display URL match its destination URL (the URL of your landing page). For example, if your destination URL is www.google.com, your display URL must also be www.google.com. The following would not be acceptable display URLs for an ad for www.google.com: www.google.co.uk - because this URL leads to a different site www.gogle.com - even though this URL simply redirects to www.google.com it is still not acceptable www.gooogle.com - because this URL leads to a page showing content identical to www.google.com
I hope you are aware that you may use ghost directories in your display URL. For instance: mysite.com/freesignup Oh and by the way, if you have multiple campaigns running and you change your display url to MISmatch your destination url, it takes quite a long time before adwords team comes along and pauses your campaigns. So you can easily get away with a few days worth of competitive advertising.
If the actual destination url is google.com/, google will allow your display url to be google.com/WhateverYou want