Dude, that sounds like a nice challenge to me! However, you should use skirmishers. Lots of them! Also, use ranged cavalry (either auxilia cavalry or any javilin or archer cavalry mercenary you can find) and use them to try to lure the elephants away from your main line. The trick is to get them so fatigued they will either rout or run amok (make sure the are far away from your main troop force by then!). This will work nicely (if you can indeed attract the ele's attention) as they will be too slow to actually keep up with light cavalry. However, if your enemy has cavalry of its own, try dealing with them first, so they will ot either kill your cavalry or keep them busy.