The switches can be in later levels.
Which, frankly, is one of the most annoying things about this otherwise great game. I spent hours on one level, probably the one you're on, going back again and again, knowing I must have missed something. Screaming in frustration, then screaming louder when I found out I couldn't unlock it in that level. The whole thing just pissed...
Don't get too upset about it.
Oh. Never mind.