The included Flash games use the following mapping:
B (right button) = enter
A (left button) = S
X (bottom button) = space
Y (top button) = backspace
L (left trigger) = D
R (right trigger) = A
When I try to reconfigure the bindings I can only select: enter, S, space, backspace, D, and A. Dunno if the selection is restricted via some configuration file or if only these keys are available in general.