Take the bolts out, turn them round and then thread them through the screw section at the back of the bar clamp. Place a 1p coin in the slot of the bar clamp in front of each of the bolts and wind the bolt on to them. Once the bar clamp is wound open enough the bars will fit without damage to them, then unwind the bolts and take them out then pop them back through the right way. This will open the bar clamp gently and without any sharp edged tools like screwdrivers or mole grips. This was the way we used to do it with Syncros stems and velocity stems BITD.