We have a long dowel hanging from the ceiling, attached with a strong carabiner, with a disc about 3-4" across at the bottom. When we get really nasty weather and the girls won't go out (and the time the run roof collapsed due to ice and snow), I core a cabbage and put the dowel through the core. The birds happily peck away at it, and no worries about anyone accidentally ingesting string. I've also used zip ties and attached a bunch of carrots all around the dowel, with similar happy flock results.
I don't know if playing gentle music actually helps boredom, too, but I have taken my old radio out the few times they've been trapped indoors and played the classical station softly. It can't hurt, anyhow.