Please let us know how it goes if you end up installing a sliding screen. I'm interested in doing the exact same thing to help center my screen (which is otherwise a bit left of center due to a stairway entrance on the right end of the wall) but not sure how doable it is of a project, especially since I would want to do it with a fairly large (120") screen.
VIDEO: Epson 5040UB | EliteScreens AEON Edge Free 110" 16x9 CineWhite Screen | Sony 55X900A
MEDIA: Oppo BDP-103 | Sony PS3 | Apple TV | FireTV
RECEIVER: Yamaha Aventage RX-A820
AUDIO: Polk RTi6 (front L/R), Polk CSi3 (center), Monitor Audio Shadow 25 (surround L/R)