Overriding a func_ entity (such as func_bombsite for a CS:S gamemode-type thing)

How would I make/replace a brush entity such as func_bombsite via Lua?

Using func_bombsite for an example. I want to make a weapon only fire in the func_bombsite, making it place a bomb. How do I keep the func_bombsite from disappearing (since it doesn’t exist in the Gmod source code, it is removed) and then check to see if the player is in said func_bombsite?

I know basic Lua, and I am working on a custom gamemode. If you’ve seen my other posts, you probably know the one.

EDIT: Duuuh, nevermind. I never realized there was a brush entity type.