This would be my vote too.
Someting like:
Ex-Employee review: Business sucks, blah-blah-blah.
Business: Sorry your employment here didn't work out, hope you are well.
(I might even just use a first name, if it weren't too identifying by being unusual)
As a potential customer, I see that and laugh, but it is polite and professional. No need to go Wendy's on them, that's too much.

