Originally Posted by
habilis
I haven't seen four stem bolts yet. I HAVE seen two pinch bolts with allen heads. Regardless, my approach would be to loosen those bolts just enough to allow the stem to turn with slight force. Make the correction and tighten the bolts sufficiently that you can't easily turn the handlebar while gripping the front wheel with your knees.
I think you misunderstood the OP. His problem isn't an off-center stem relative to the front tire. His handlebar is off center in the handlebar clamp and 4-bolt handlebar clamps are very common.