Hi Andrew,
This is very straight forward, you need to use memories and Effects Dissolve. They can then be called from a CC if you want.
Create the first scene (maybe the split screen) and save it in a memory location for ME 1, when you make the save set the recall attribute to EffDiss. Now reset one of the DVEs to full screen and save that in another mem location - again making sure the recall attribute is EffDiss. now by recalling each memory the DVE will smoothly transition between each location.
You can also adjust the rate of the effect etc. by modifying it in the memory attributes, you can them create a CC macro that calls the first memory and transitions to the next with either a timed pause or a manual hold.
Also if you are using MiniME's you can create the same effect without using a main ME.
Nigel
#Carbonite