Yup, a good workaround. I'm not sure that can be countered... what about a correlation between who pays and in return get's voted on a post? That would remove most of the efforts, and only those who use alt accounts to bypass it would be doing so. Or just have a list of known bidbots, and annul the author rewards that get applied through bidbot votes and re-allocate those rewards to the pool. Then you don't even need the memo at all.
The homepage change is so simple, yet why haven't the top witnesses agreed to change it? I think most of them are indifferent to vote selling, or actually want it. Also a change of trending page to be measured some other way would also be easy to do. Yet, it's not being done...
Accounts that have large or many delegations can be suspect as a first filter to look into. Then, transactions can be looked at to see if they receive transfers often and upvote same people who send the transfers. This would identify a vast majority of bots. Checking for refunds/returns is also a cross validation. All it takes is some activity to catch a bidbot account.
Changing the default front page is something that should have been done a year ago... :/