One way is to loosen the nut so it's maybe 1/8" away from the wheel. Sit in the seat with your knees under the wheel and exert lots of upward pressure on the wheel. Then carefully whack the nut with a 2-3# hand sledge.
That might damage the chrome, so substitute a different nut. Usually you try to run the nut just flush with the end of the steering shaft so you're hitting both at once.
We used to do that with cars and tractors both, worked pretty well if no puller around. YMMV. Also, use a real penetrant, not WD.
Jim