After some celebration to the 1-2 for Ferrari at Imola earlier today, here comes the info in english
1. Download and start AFCAD
2. Choose 'Open Airport' from the 'File' menu
3. Choose the airport you wish to change (like KJFK)
4. Go to the 'Lists' menu and choose 'Runways'
5. Mark the longest one (which happens to be the default active one in FS) and click 'Properties'
6. Set 'Restrictions' to 'Closed' on both ends of the runway
7. Click 'OK' and then close the 'Runway list' window, save and start flightsim and watch the wounders of dual runways