Yiddish: It's as helpful as cupping a corpse.

It's useless, ineffective.  SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten.  Cupping is a traditional healing practice in which cups are used to create suction on the skin in order to mobilize the flow of blood or stagnant energy. Whether one believes in its efficacy or not, it clearly can't help a dead person.  (see also)  Compare:

‎‎.דעם רשע העלפֿט אַזוי מוסר זאָגן ווי אַ טויטן באַנקעס
Dem roshe helft azoy muser zogn vi a toytn bankes.
Moralizing to a criminal is as effective as cupping a corpse.

SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh

עס העלפֿט ווי אַ טויטן באַנקעס.

Es helft vi a toytn bankes.

It's as helpful as cupping a corpse.