A solution came to me in the shower this morning.
I'm going to replace the whole of the support page with simple text with two options.
* If your problem is with a site that you were visiting and don't own, click here.
* If your problem is with installing and configuring one of our programs on a site that you own, then click here.
The second links to most of the text from the current support web page. The first links to a page containing (simple!) instructions on how to contact the owner of a web site.
That feels like the right solution to me.