You can do this with slice transform but when going from a full screen to a split screen like this, you're going to get a "cut" and not a smooth transition or fade/scale to have the image fit in its respected spot.
put your content on layer 1 and your add on layer 2, and your background image or content on layer 3.
create your slices in advanced output. 1 slice being full screen and the other 2 slices being the add position (scaled) and the content (scaled), keep the third slice full screen for your background.
assign input selections for each slice, full screen gets layer 3 and the other 2 slices gets layer 1 and layer 2
add slice transform to layer 1 and 2 and bypass it.
map a keyboard shortcut to fire clips 2 and 3
map a keyboard shortcut to un-bypass the 2 slice transform fx.
map another button to kill layers 2 and 3.
when you press the fire clips and slice transform button, you should get the desired look. press the slice transform button again and the kill layers 2 and 3 button to get back to your original look
again, this is going to be a hard cut, and not smooth.