What about Vegemite Whip??!!
BTW, I wouldnt be surprised if the salts in the carbonation didn't thicken the Carragennan thickner in the Dole Whip mix, causing the coagulation to occur in your first experiment. If you could first well mix the Dole Mix to a thinner more uniform consistancy, then add the carbonation or carbonated liquid with less final viscocity, it may work better. A stick blender may help in about 3 times the water you started with. Then perhaps using a lemon lime soda (I know, you would rather use the beautifull machine taking up valuble real estate on your counter) would work.
~Bob