What I would do would be:
1. find out what ip their company uses to access shit. It will usually be a single block of ips.
2. Through a script into the page that when it is hit from one of their ips shows the page they are expecting.
3. When it is not one of their ips show a different page, perhaps with the story about how they are ripping you off, or extolling the virtues of one of their competitors or whatever other fun things you could think of.
It can be wonderfully fun when people give you control of their content by hotlinking.
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