Setting World Props to prop_physics

How can I make the props who’s class just displays as worldspawn, as a prop_physics class?

You know, the props in the Half Life 2 Campaign, when using the trace command, the entities don’t show up as a prop_physics (even though they are, as you can manipulate them with your physics gun). How can I have a script that sets them all as the prop_physics class? Thanks.