We read in Rashi (‘Avoda Zara 18b) that Rabbi Meir commanded one of his Talmidim to go and seduce his wife Beruriah. My question is, independently of the content of that story, how Rabbi Meir could do such a thing, as it is forbidden to "put a stumbling block before the blind" (Vayikra 19:14).

Your question assumes he seduced her to the extent she sinned. It is not necessarily what Rashi says, it says agreed not that she sinned. This is supported by the Ben Yehoyada ibid, who asks two questions on Rashi's comment – how is it Bruriya, being such a righteous woman, was seduced; and how is it that Rabbi Meir put his student to the test and transgressing the prohibition of placing a stumbling block before the blind, it is clear therefore that the Ben Yehoyada did not find what Rabbi Meir to Bruriya a problem of "Lifnei Iver"