Nice theory, DT. But logically, why would Fredo want to involve Anthony in the simple matter of opening the drapes--something Fredo would have done easily and without being seen? As a family member, he'd have complete run of the house. If he involved Anthony, he'd have had an "accomplice" who could easily have ratted him out. After the shooting, we seen him, frightened to death and being clutched by Connie. It'd be natural for him to blurt out, "Why did Uncle Fredo tell me to open the drapes?"
"Ghost of Tessio"--now, there's a title for another film in the GF series!