Heh... just hold down to lean back. Start off going slow, then lean back and hit the gas, and your front wheel will go up. Be sure not to lean back too far though, because you will fall over and take damage. It's kind of hard to do wheelies on PCJ's, and it's really hard to do them on the big harley-type bikes, but Sanchez's are really good for wheelies.
Sanchez is also my favorite vehicle in that game, aside from the apache helicopters.
