That'll be a waste of time and I advice you shouldn't since, the user has the authority to delete any post on his self moderated thread. The best thing you can do, to make the scam accusation warning more visible was to create a flag (and i can see you have done so, that's good) now update the OP with link to the flag which is; https://bitcointalk.org/index.php?action=trust;flag=670 to request for support from DT members to make the flag active.
When the flag become active, a warning will appear on all his created thread meaning you don't have to keep posting on his self moderated thread (which by the way it's useless since he can just delete the posts).