I tried but couldn't redirect back to my website as they stripped / rewrote all JS.

You could have a "stolen content" pure HTML/CSS banner that gets removed by Javascript. Only proxy site visitors will see the banner because the proxy deleted the Javascript.

some people like me will see the "stolen content" banner on the original website. And attackers can trivially remove it as soon as they get aware of it.

Would it be possible to hide a hash/encoded URL somewhere in JS and delete the site/redirect if the hash/encoded URL contained something unexpected?