Any way to spawn entites Hammer doesn't know about?

NameUser

L1: Registered
Sep 15, 2011
45
1
I've made a 'fool around' map for a few friends, and have been looking to update it recently. I wanted to have a room that spawns tf_zombies. I read up on how to spawn entities, but I have no clue how as Hammer doesn't know they exist it seems (IRC, last Source SDK update was before they were added). Any way to force it to spawn an entity by it's name?