I have one of the foam pieces in one of my exoterra cages. It's just held in place with friction from being pushed into place. I left it there because it will help insulate the cage and helps keep things hidden for the snake.

I doubt your BP will stay there, probably once it's settled into its new home it will stay in the hides. Make sure your hides aren't too big, some fake plants and things help the snake hide as it moves around so that can also help.