It is well known that if a person begins reciting a Beracha that is not required, and he realizes his mistake after reciting the words "Baruch Ata Hashem," he has the possibility of avoiding an accidental utterance of Hashem's Name in vain. He can do this by immediately reciting the words "Lamedeni Hukecha," which has the effect of turning his words into a Biblical verse. The phrase "Baruch Ata Hashem Lamedeni Hukecha" is a verse in Tehillim (119:12), and so by adding the words "Lamedeni Hukecha," one transforms his recitation of "Baruch Ata Hashem" into the first words of a verse, such that he is not considered to have recited Hashem's Name in vain. One common case is when a person recites a Beracha over food during a meal, forgetting that he had recited "Ha'mosi" over bread and thus does not need to recite a Beracha over the various foods eaten during the meal. If he began reciting a Beracha, and after saying "Baruch Ata Hashem" he realized his mistake, he should quickly add the words "Lamedeni Hukecha." Less known, however, is the option that one has even if he realized his mistake later, after he already recited the words "Elokenu Melech Ha'olam." At this point, of course, it is too late to turn his mistakenly-recited words into a verse from the Tanach. What he can do, however, is to recite a Beracha which, although we do not customarily recite, some Rishonim (early Medieval scholars) had the practice of reciting. The Bet Yosef brings that some earlier Rabbis would include in the Birkot Ha'shahar (morning blessings) a number of Berachot which do not appear in other sources. For example, some recited a Beracha "Baruch Ata Hashem…Magbi'ah Shefalim," praising Hashem for raising the downtrodden. Another Beracha that some Rabbis recited was "Baruch Ata Hashem…Somech Nofelim," praising Hashem for supporting those who are falling. The Bet Yosef disapproves of this practice, despite the fact that these Berachot were included in several editions of the Siddur in Spain. He notes that these Berachot are mentioned nowhere in the Talmud, and we do not have the authority to introduce our own Berachot. However, the Mishmeret Shalom writes that the fact that some early Rabbis advocated for the recitation of these Berachot allows a person the opportunity to avoid a mistaken recitation of Hashem's Name in vain if he had begun reciting an unwarranted Beracha. If a person realized after reciting the words "Baruch Ata Hashem Elokenu Melech Ha'olam" that his Beracha is not needed, he should immediately recite the words "Magbi'ah Shefalim" or "Somech Nofelim." This way, at least according to some Rabbis, he had recited a legitimate Beracha, and has not recited G-d's Name in vain. Summary: If a person began reciting a Beracha, and after saying the words "Baruch Ata Hashem" he realizes that the Beracha is not warranted, he should immediately say "Lamedeni Hukecha," so he will be considered to have recited a verse, instead of having recited G-d's Name in vain. If he realized his mistake only after he said "…Elokenu Melech Ha'olam," he should immediately add the words "Magbi'ah Shefalim" or "Somech Nofelim," as these are Berachot which some Rabbis had the practice of reciting each day. Although we do not follow this custom, it is preferable to add these words in this case so that at least according to these Rabbis, the person has recited a legitimate Beracha and has not recited G-d's Name in vain.