Yeah there is just one piece of foam that goes across the entire footbed on the Limiteds. You have to pop the snaps by the heel (I think those are the ones you're talking about?) to get to the disc. The foam just bends and creases the first time you flip it up. You can get at them from the top, but they didn't free the gas pedal when undone.
There are instructions, but they're useless. They probably package the same little booklet with every binding they sell; the "gas pedal adjustment" instructions are a picture of the bindings with an arrow pointing to the gas pedal :/