Proper method to use referral data for a PHP based website

We manage an online enrollment site. Customers can ONLY enroll in our program if they come through an agent URL which currently has the format:

www.site.com?Agent=AGENTID

While this approach works, it makes it very difficult for our agents to simply send 开发者_JAVA技巧out or 'tell' their URL to a potential customer.

I have tossed around the idea of making a subdomain redirect to the format above but our Media temple configuration requires major changes to the apache conf file which we are trying to avoid.

Similarly, I think we could just direct customers to www.site.com/agentid but run into the issue where /agentid will be treated as a page instead of an ID (and other times www.site.com/pagetitle may actually be used for a real page).

Anybody ever had a similar issue in the past? I'd be happy to hear any opinions for the best approach.

Can you create a subdomain only for referrals, and setup url rewriting on that subdomain? Then it would not conflict with any pages on the main site. Something like agents.site.com/agentid.

If you have AllowOverwrite and mod_rewrite activated, then you can create a redirect from www.site.com/agentid to your format without messing with the core apache conf, by placing a rewrite rule in a .htaccess in your main web directory.

I do not think there are any other solution without changing the apache configuration.