I've had that problem. The simple fix is so turn the bars upside down, to where the "rise" bend is facing the opening on the bottom of stem. Throw a rag over the end of the bars, grab onto the stem and bang it with a hammer. A few swift, strong hits with a hammer get's it through.

Seems drastatic but it does no harm to either components, other than maybe some scratches on the bars from the rubbing, no big deal.