Hi, I fit mdf doors with butt hinges into softwood frames all the time and sometimes mdf frames when I need a wide side panel. Like someone said use long 45mm-50mm thin screws and pilot them full depth with drill bit that just lets the thread cut into the mdf. Use butt hinges with staggered holes on the leaves of the hinges and when you pilot them angle the pilot holes so that you drill slightly accross the compressed layers of mdf. Also the hinges need to be sunk in and not surface mounted. If you use all these techniques then you will avoid splitting the mdf. If you hang wardrobe doors use three hinges per door. I have checked up on doors hung like this and there has been no problems. If you do not follow all these steps then they will split! The ideas of using dowels etc.. sound good.The main thing is to avoid the screws going in straight as any pressure splits the mdf.