Umm, didn't someone post this not too long ago?
Then write some PHP code to randomly switch some tubgirl or 'I stole this image' type images. Build a rotation of like 5 pix and make sure that the regular pic is in the rotation. So sometimes he sees the regular one and sometimes not. Even better: See if you can track down his IP (from your server logs) and make the regular image appear for his IP only. All of his customers get something else.
Umm, didn't someone post this not too long ago?
Just replace the hotlinked images with Goatse, but only during business hours so the guy thinks it's HIS server, haha!