How do I track trial sign-ups using Goals in Google Analytics

When someone signs up to free BC trial via my website, the sign up and the completion page have the same URL: http://practicepl.us/signup/obb.aspx?SPID=46285 which means I cannot use Goals in Google Analytics to track how many trial sign ups I get each month.

To record this as a goal completion in Google Analytics I need a different URL for the completion page or be able to run some javascript to trigger an event.

Has anyone achieved this or know if it's possible?

Thanks in advance

Matt