You're basically asking to show ads that are even more irrelevant and useless to your users?
The best ads for publishers and users are ones that are relevant. If you want to display something that is irrelevant to the user and ineffective for the advertiser, you might as well not display ads at all and avoid annoying your users.
You can, there are plenty of XML feed providers who will provide you an XML of ads relevant to the keywords you provide, which you collect server side and display to your users.
The best ads for publishers and users are ones that are relevant. If you want to display something that is irrelevant to the user and ineffective for the advertiser, you might as well not display ads at all and avoid annoying your users.