You could go for a 2-step cyanotype - coat the paper with the ferric ammonium citrate and let it dry, store it, expose it, and then develop it in the potassium ferricyanide. It would probably fog less in humid environments (depending on how the paper reacts to the FAC). Haven't tried it, but it'll also give you 2-3 stops improvement on exposure time.

http://jorj.org/blog/?p=2541

(Works for Cyano II as well.)