Allow object to move with arrows keys, but disable up

I'm making a biking game and want to be able to turn my object left and right with the arrow keys, however I want my forwards motion to be tied to a button, say the A button, so that when the user presses A, the biker pedals a half rotation and goes forward a little ways, and then the user presses A again and he'll do it again, etc. to simulate riding a bike.

Because of this, i don't want the bike to be controlled at all by the forward key, because it would make the bike look like it's just sliding on ice. Anyway to maintain the left/right controls to rotate the bike, but disable the up arrow from working entirely?

There is one way that I know to do that, click on the events menu, choose when a key is pressed, then right click it and select change to while a key is held. Then select right arrow, and say 'bike turn right x revolutions' to turn it. Same thing with the left key and turn. Don't use the 'let arrow keys control <object>' event.