Most stems have slighly angled cuts to the clamp area (usually at the bottom of the clamp, that will let you manuever the bar bends through without any jamming. try looking for these angled notches and slowly slip the bar through. These cuts will let the inside of the curve go through because it shortens the clamping tube in that area. I have not run across a bar that won't go through a stem without any spreading of the clamp. It is not to say that there could be bars out there with more severe bends (ergo bars) that might require spreading if there is no way it would go through.

Chombi