Hmm I like the suggestions, but I have some reservations:
This says “he gave me flowers,” which is the opposite of the intended meaning from the OP (I know you’re aware, just making it clear for everyone else). But you’re right, if the goal was to say he gave me flowers, this is more natural than just saying 上げた, which would mean he gave it to someone (probably other than the speaker).
This works great in that the one receiving the flowers is 彼, as intended. I’m just left with the impression that this would not imply that the speaker was the one who gave the flowers because もらう emphasizes the receiver and de-emphasizes the giver, but then that would mean de-emphasizing oneself. It seems to me, then that this sentence is just short for:
彼はかっこよすぎるから、誰かに花をもらった, which means he received a flower (from someone, probably other than me). You could, of course, say 私に花をもらった, but then this would emphasize that he got the flowers from you, rather than someone else. http://www.guidetojapanese.org/favor.html