All those threads need to be warned or is that something you don't seem to understand. Why would you want to remove the warnings on his threads to help him?
A much easier and more effective way would be to create a flaga gainst the user and ask a couple of DT members to support it so that it becomes active. I see you haven't done it yet but once it's active. It will display a red banner with a warning at the top of every topic the scammer made.