Because the blowing of a shofar in Elul is a minhag (as per the comments) are there any requirements/rules that limit it? Must it be blown from a kosher shofar (if not, could it be blown from a non-shofar)? Must it be blown in the same way as a blowing for the mitzvah -- from the side of the mouth? Does the person who blows it have to meet the same standards (not be deaf, go to mikvah etc)?
While the blowing is a practice (and has various historical sources and precedents) so we might WANT it to mirror the "real" blowing in all ways, it is still not a mitzvah, so what are the parameters/limitations to it?