Mario Kart Wii Controls

[Hoshi]

When I play mariokart wii on the wii with the steer, i have to make the steer go up quick when my cart is in the air to do a sort of stunt, so that i get a sort of mini turbo when i land. Now when i play i on dolphin and use my keyboard as gc controller which button do i need to press to perform the same trick?