Might I suggest a spin on this: instead of blocking the IPs, consider serving up different content to those IPs.
You could make a page that shames their domain name for stealing content. You could make a redirect page that redirects people to your website. Or you could make a page with absolutely disgusting content. I think it would discourage them from playing the cat and mouse game with you and fixing it by getting new IPs.
You could make a page that shames their domain name for stealing content. You could make a redirect page that redirects people to your website. Or you could make a page with absolutely disgusting content. I think it would discourage them from playing the cat and mouse game with you and fixing it by getting new IPs.