Well, one way you could do it is through my tutorial here...
http://www.cncseries.com/content/?523
Essentially it allows you to replace a unit with another unit, transfering the energy and veterency through using a weapon.
The disadvantage to doing it this way is that it counts as a kill, which means either you stick with an extra kill being counted or you completely ommit that unit from the score figures, also, you don't retain the selection of the unit which gets replaced. Also, the effect doesn't fair well with transport units as you can tell.
Nonetheless, when done properly the swap is seemless and has endless possibilities, e.g. as in my tutorial the trigger weapon can be self inflicting, allowing for a deploy unit effect, or the weapon can be triggered by another unit or by a special power.