a 404 script is the way I would handle it.
Modify what the server does when it finds a page that doesn't exist.
Currently the server issues 404 headers and displays a brain dead message
about not being able to find the page. Change that so that the server
issues 200 headers (tricking the client which has "friendly error message"
enabled) and pick off the part after the .com/ and do a look up for the
item. If found, proceed as expected, it not found display, a brain dead 404
How do you modify the server?
Either modify the 404 directive in Apache or one of the other lesser
setup a .htaccess file on their domain
The .htaccess has a line that says:
ErrorDocument 404 /new.php
Which means when the page is not found display the page /new.php
Build your product look up and place it in the file new404.php
Be sure that the first line of new.php is
<?header("HTTP/1.0 200 OK");
That's the header that tricks the "Friendly Error Message"
I wish I had come across this info as easily as you just did!