First put the troops you want moved to the other city into a valley. Next send 1 scout and a hero to that valley from the city you want the troops to move to. Then once scout and hero have arrived go to valley on map while in the city you want them to go to and recall from the valley. Your troops will go to that city at the speed of the scout.
You must recall from the valley or the troops will take 10 times as long.
Example:
I want to move 500 ballistas from city A to city B
I put the ballistas in Valley
I go to City B and send 1 scout and hero to the Valley I put ballistas in.
While still in City B I go to the Valley on the map and click enter. then hit recall. Ballistas and one scout and hero will return to City B at rate of scout movement.