Use APP as a Tilt-Shift Lens
You can use APP in a similar way as a tilt-shift lens, see <http://forum.autopano.net/t1232-perspective-control-lenses> about halfway down the thread is a discussion of this.
And a note from http://en.wiki.autopano.net/Geometry_Editing : Note that when setting the vertical center (i.e. placing the horizon at the location of the horizontal grey line), the click location should be located at the camera's height, unless you are looking for a low angle shot (verticals converging up) or a high angle shot (verticals converging down). To move the horizon up or down it is best to use the Set Verticals tool described in the next paragraph.