The best approach is to use clients that have filters by WoT, or that have filters by strings in the user profile (just silence all users that have "reply guy" in their profile name or description). But those are few (AFAIK only iOS clients have those filters). More clients should be implementing those filters, and more sophisticated filters. Filtering spam should be on the client, not the relay side!

But, if using any of those clients is not an option to you, the second best solution is running a relay of your own that has such filters. A WoT relay or a relay that implements filters.

Failing that (i.e. you have no server or virtual machine where to run them), use one of the publicly available relays that implement WoT or filters.