If I wanted to be "clever" I might offer the following, TRY, however that is not my intention.
Actually, the 90 day period you mentioned, one published item per quarter per individual applies only to Letters To The Editor, published in the "hard copy" of the P-G. Blog comments and or responses to published letters, cartoons and or editorials are exempted, as I understand. Also exempted are an item, shall we call them "overflow" letters, sometimes appearing in the on-line edition of Thursdays P-G.
Personally speaking, for whatever that might be worth, I don't agree with the "quota" system, but then I don't own the paper either. If I did, respecting certain aspects of things, their editorial policy would undergo a very significant change.