Catalyzes the methyl transfer from S-adenosyl-methionine to the methylene group of 24-methylene lophenol to form 24-ethylidene lophenol. 24-methylidenelophenol + S-adenosyl-L-methionine = (Z)-24-ethylidenelophenol + H(+) + S-adenosyl-L-homocysteine Steroid biosynthesis; sterol biosynthesis. Belongs to the class I-like SAM-binding methyltransferase superfamily. Erg6/SMT family.