How do you put canned frosting on a cake without tearing up the cake?

It’s my son’s birthday. My ex-wife, his mother, doesn’t even know the boiling point of water, much less have the technical skill to actually boil it.
So I make him a birthday cake.
I use a mix for the cake, and one of those jars of frosting to put on it. I am sure I could get a better result if I did it from scratch, but I don’t have that kind of time.
So, is there some trick that I can use to frost the cake, so that it goes on smooth without rolling up and pulling the cake apart?