vero, Roberte. ubi amicos mei casae advocavi, cogito 'nemo aderit'. sed ecce! omnis amicarum adsunt. tum 'gratias ago vobis, non nemo adest' dicam aut sicut 'in ipsa curia non nemo hostis est' Cicero. quoque tu, Brianus. 'non bona non est' et 'non sumus nescii' dicas..

Not exactly the same thing, but there is a Greek poetic device called "litotes" which occurs in Latin poetry. Catullus, Ovid, and Horace most notably. Sorry I don't have any examples on-hand, but an English example would be "That is not ungood," meaning "It is good," or "We don't not know," meaning "We do know."