You can place ACH blocks on accounts, at some banks anyway. I don’t know if the bank will give you the transaction information if a transfer is attempted. If they will, shouldn’t it be possible to set up a honeypot account in order to get the ACH info? Is that info enough to trace back to the spammers?

This opens up other legal questions though. It’s entirely possible that you could then be on the hook for non payment or something.