Another possible avenue to explore, if you haven't already looked into it: I notice that a number of these accounts (i) are new; (ii) have their recovery account set to @steem; and (iii) are basically unfunded except for some delegated SP.
I haven't tracked back the source of the delegations, but I assume they're conducting their abuse with SP that's delegated by Steemit, Inc. at account creation time. Is there a process to report abusive accounts so that Steemit, Inc. can revoke the initial steempower delegation? If not, can one be established?
We've already reported many account to Steemit Inc. and they did take off their delegation in a timely manner.