I'm not part of the committee running the jam, but why not just use [Z] for "A" and [X] for "B"? It's fairy common for GB and NES games and works rather well. Is there a reason that space and esc would be more useful options?
You are allowed to bind your keyboard however you like. I have seen concerns raised over using the Z key however, as some keyboards will ignore the Z key depending on the number of other keyboard inputs currently given, and also the AZERTY users will have it significantly displaced.