On https://metabrainz.org/donate we say "Due to the increased unreliability of the US Postal Service we have stopped accepting paper checks. Sorry!"

That is not quite true - in fact we get and cash DAF checks several times a year. It is true though that it's an inconvenient method and it involves higher fees than others (plus the risk of losing the check). So I'd suggest replacing that with:

"Due to the increased unreliability of the US Postal Service and the relatively large fees involved, we ask you to only send a paper check if it is the only possible option. Due to the fees, we will not cash checks for less than $25."

And then having the address for checks behind a button like we do for the contact email, like: "I confirm I only have cheques as an option".