What? Aren't flaming pigs good enough for you?
I don't think you can but I also don't think that its historically accurate either. I don't think they did that back then as the plague didn't happen until Medeival times (and no, you couldn't do it in Medeival: Total War either
)
AS for the War Elephants... download the Demo and you'll see what I mean. Watching a few elephants decimate an entire unit of Legionnaires ticklesme in funny places...