From Ezras Torah:
At Maariv of Sunday night Dec. 4, 4 Kislev, we begin to include Vesain Tal Umatar into the Shemonah Esrei. If one became aware, after he had completed the Bracha Mevaraich Hashanim, that he had omitted Vesain Tal Umatar he should wait to insert it right before Ki Ata Shomeah of Shema Koleinu. If he had already completed the Bracha Shomeah Tfilah, he may insert it before saying "Retzei". If he had already begun "Retzei" he must return to the Bracha "Boraich Aleinu", which is the proper place for Vesain Tal Umatar. If he had already completed the Shemonah Esrei and stepped backward, then he must repeat the entire Shemonah Esrei. In any situation in which a person must repeat the entire Shemonah Esrei, he may fulfill his obligation by listening to every word of the Chazzan's Repetition from begining to end, with the intention of thus fulfilling his obligation.It seems the good Lord anticipated our requests and gave us what to shovel this morning. It should always be li-vrakhah ve-lo li-klalah.