Yeah I am at uni right now so cannot check, but I am 99% sure on the stegadon page when it is talking about characters on stegadons it says 1-4 hits steg, 5 hits crew, 6 hits character... That is the way you would do it. No LoS since it is not a unit. Hmmm, I wonder if the character on steg can get LoS if the steg has joined a unit? Are there rules concerning monstrous mounts in a unit? My guess is they can be picked out, but I dont know without having my rulebook here...