Turns out you can do this with an unmodded keybord! Just map left LS right and LS left to buttons and DPad to other buttons. So that basically confirms that this is crossplay tournament legal.
Right now my current keyboard layout is:
A: DPad left
S: DPad down
D: Dpad right
Space: DPad up
J: LS left
K: Right Punch
L: LS right
N: Left Punch
M: Left Kick
Comma: Right Kick
This also lets me press the kick buttons with the correct fingers, since the keys are closer together and the bottom row of the keyboard is offset.