o... k... so, let me think here.
You have Steam. You can use Steam to play Blockland with your key, right?
I think Badspot can flag keys as "steam-only" so that he can deal with the keysharing problem without revoking the key, but in the past, some people whose keys were supposedly flagged "steam-only" found them completely revoked instead. Not sure why.
Regardless, I guess if the issue is serious enough that you're willing to risk losing your key (you DID post about it in a place where Badspot can see it, after all), I'd say your best bet would be to ask Badspot to flag your key as steam-only, so that you could only play Blockland through your own Steam account.