This is a very difficult shot, but it can be done.

The most succesfull approach for me has been to use a 60 degree wedge, open the face completely and hit with a full swing, trying to keep the club head moving along the slope even after hitting the ball (club is going down!).

The ball will not travel very far and not very high (because of the downhill lie) but because I use an open lob wedge, it will clear the hazard and stop fairly quickly.