But it probably wouldn't work anyway. If a judge agrees that there is a need for a secret warrant, it's serious enough (aka national security) that the judge will tell you to continue doing business as usual, including posting your weekly canary.
There is no harm to you of posting an incorrect warrant canary and if that's the only objection you have, the judge will be happy to give you immunity on that point.
If you refuse to do so, expect to be held in contempt or similar coercion technique.
Bottom line: it doesn't work. Too bad.