The barrels don't usually leave quite as much unsupported on the smaller diameter case, but it can happen, especially with +P loads. The 9 mm taper continues to the rim, so the rim is about 0.004" wider than the body at the datum 0.200" forward of the back end of the case head, technically making it a "semi-rimmed" case, but only very slightly so. The rim dimension has a -0.010" tolerance, while the 0.200" datum has a -0.007" tolerance, making the minimum rim only 0.001" larger than the minimum datum diameter. (See here
So, you can take the 9 mm Lee Factory Crimp Die, unscrew the crimp ring retainer cap and remove the crimp ring, then just use their bulge buster kit to push the 9 mm cases through. It'll take maximum dimension rims down slightly, but they will still work just fine. Worst case you'd have to deuburr the rim with a quick swipe over a flat file.