Here is what i do and it works all the time, send him this below email and include some fake email id of attorney in cc, or To, any email id just make it look like you are involving attorney.
Dear (theirwebsite) owner,
It has been brought to my attention that verbage found on your website, (theirwesbsite) is a potential plagiarism of our company website, (yourwebsite). Such verbage was primarily found on your ?all? pages. Please be advised that such verbage has been in place and used by my company exclusively throughout multiple states for over 10 years and is copyright protected.
Please cease and desist use of such verbage immediately. Thank you for your cooperation.
Sincerely,