Last post I raised the possibility of a new chumra of having to lein zachor yourself because mitzvah bo yoseir mi'bshlucho. I want to throw a lomdish twist out there as a way to avoid this conclusion even granting my assumptions. Step 1: Seems that mitzvah bo yoseir mi'bshlucho applies only where a mitzvah is a chovas hagavra. If the mitzvah is simply for some effect to be produced (chovas hacheftza), what difference does it make who does the mitzvah? Step 2: Maybe the chiyuv of zachor is not a chovas hagavra to read the parsha, but a chovas hacheftza on the parsha to be read. (So why can't a katan lein? Because a katan's keri'ah is not a ma'aseh mitzvah.) If I'm not on thin enough ice already, let me take it to step 3: the reason the first Mishna in Megillah uses the term "megilah nikreis" instead of the more direct "korin es hamegilah" (as is asked by the Ritva, Turei Even, others) is because kri'as hamegilah is a kiyum in zechiras amalek and is therefore also a chovas hacheftza ro be read, not a chiyuv on the gavra of "korin..."
But enough already, because we are up to Parshas Parah. "Zos chukas haTorah asher tzivah Hashem leimor. Dabeir el Bnei Yisrael..." Why the double language of "leimor" followed again by "dabeir?" Chasam Sofer writes that this is a hint that the dibur itself, the very reading of the parsha, is what Hashem commanded Moshe to tell the people to do. From here we have an allusion to the fact that (according to some views) the kri'ah is a din d'oraysa.