I'm not sure about siege towers either, they ARE rather clumsy...

Trebubuchets on the other hand could easily (when weighted and modded right) toss one or two specially trained elite soldiers up on the elephants back.

Granted, not over any long distances, but as a last defense when the elephants gets to close for comfort to your battle line.

I mean, try to keep it realistic, mouse brigades and the other rants just had to be a joke, right?

I vision this trebuchet unit to have some selected "gun-ho" troops specially trained to clear the hut on the elephants and then take controll, they must of course have some sort of padded armour to sustain the initial crash down on the elephant and only light weapons for obvious reasons).