Page 28 covers how to specify a script, script parameter and variable in the URL that will run when loaded.
However make sure that you setup your security accordingly to handle access accordingly.
It would also be possible via CWP by using $_GET or $_POST PHP commands to pass in and pull up the records.
Barcode scanning to pull up records would indeed be a better experience on FileMaker Go than in webdirect. Although it's possible using a keyboard input barcode scanner, the native abilities of FMGo are far superior.