In a recent interview, filmmakers the Coen brothers said that when silent-film maker Hal Roach had a story conference, he’d bring in an inmate from the local insane asylum to join in. This person was known as “the wildie” because when his opinion was solicited he’d come up with something totally wild.
His ideas were not usable but they would spur wilder (but productive) thinking on the part of the others in the meeting.
No, I’m not suggesting you try to bring an insane person into your meeting, but rather that you ask someone to play that role–to blurt out whatever crazy idea they have. It’s then the job of the rest of you to figure out how turn that into something usable, even if that means changing it totally.
For sure it’ll make your meetings more interesting!