Design question: Monsters that act like a class

[frumple]

Just a question folks.

When you are trying to code up a monster that has the abilities of a class, such as a Witch's hexes or Alchemist's discoveries, how do you go about it?

Do you make custom racial abilities of every hex/discovery, etc. the monster has access to? Have you figured a way to use the class's abilities directly (which in my experience leads to issues since races do not have fields such as xTotLevel, etc.)?

I am just trying to figure about the best way to do this that future proofs the creature for when more of a class ability gets added.