How do I get cool whip frosting to go on smoothly?

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I am making a jell-o poke cake for the 4th, and i just want to use cool whip as thefrosting. However, I want it to be very smooth (so I can add blueberries and strawberryslices to make the cake look like a flag).. How can I make the cool whip go on smoothly, like in a sheet? Can I let the cool whip warm to room temperature, pour,then re-chill? Any ideas are appreciated.