there's no way to add a Boolean to a prop because there's no way to add bones to a Prop.
When I say import it into a model, I really mean import it into a model. Not as a prop.
-Open a new model window.
->Plugins>Import>STL or whatever polygon format works best.
Yes, it will take a long time for a big model. Let it go overnight if it needs to. When it's done you have an A:M mesh you can add bones and Boolean cutters to.