How to Hang Projector Screen from ceiling against wall?
Rather that attaching into the drywall or cobbling up short mounting blocks I would strongly recommend that you mount a board to all the existing studs that is just a bit longer than the width of your screen. 

This board can be a straight forward 1x6 pine board (actual dimensions 0.75" x 5.5"). Since you want the screen up near the ceiling anyway just slide the board all the way up against the ceiling and attach it with screws right through the drywall and into the studs. This will make a nice sturdy place to attach the hangers for the screen. Once it is all attached in place the board can have holes filled with filler or spackle. Then prime and paint to a color that matches the wall. 

Note that once the screen is hung in front of the board it will hardly be noticed that the board is there and it will still look nicer than other kludge solutions.