I've been searching for a way to get Fun 16 down to four builders, but so far I've had no luck. A simple "Tame 20 glitch + nuke glitch" solution looks like it comes a few lemmings short, and with the exit right on top of that pillar, there's very little space to create a path upwards for the crowd. But I wouldn't rule out some sort of "Tame 13-like" solution...