Don't get your hopes up. Laws are interpreted and applied by humans. If the order says you can't tell others you got the letter, no amount of information-theoretic trickery gets around that.

This can require you to lie, and I hate such laws, but that only happens if you deliberately box yourself in by setting up a warrant canary. You can avoid lying by sticking to a policy of "we cannot comment on whether we have received a request with a gag order".