ColdFusion's documentation states
Another option available is to use a URL parameter mode=debug. The URL would look like this www.allaire.com?mode=debug. This URL will display debug information whether you have debug information turned on or off in the administrator.
http://helpx.adobe.com/coldfusion/kb/coldfusion-debug-information-using-mode.html
The documentation does not list the ColdFusion version number and it does not seem to work in CF 9.01.
Does this still work? (It sounds like a security risk)