-When stuck at the end when at Turin airport, turn around and go between the two Mafia cars, up the dirt pile, and over the fence. The Mafia will not follow you. Follow the path and you will end up at the hideout.
-Ditch the Mafia fasty by going to a big mound by the fence in the corner. An intermission sequence will show the jump. After that, drive back to HQ using the hidden road. Do not worry -- it ends at the mansion. Practice this jump in free drive mode before attempting it.