Another way to force the artillery crew to quickly abandon their machines is to tell them to withdraw. They'll start to scarper, but you can just tell them to do something else and they'll no longer rout but will be free to move around and command. You can then click on the artillery pieces to have them use them again.

Also, I believe artillery crews can use any abandoned artillery weapons that are the same as the ones they were originally using. Eg: if you have 3 scorpion units that are unmanned, any of the 3 crews can use any of the scorpions.


Finally, if you want some fun with scorpions, ballistas etc, do a custom battle in the Numidian basin. It's the one shaped like a large basin with a hill in the middle. Give yourself maximum scorpions/ballista or whatever and give your foe a few units of pikemen or elephants. Set your units at the back of the map on the ridge, so that the enemy has to march over the hill and then back down and up again before they can hit you. Put fire at will mode on and watch your ballistae obliterate the enemy before they can touch you. Always a laugh!