Mainely Rat Rescue recommends the car ride, as well, especially if you drive on a windy road with the radio turned up. The other thing they suggest is putting the rats in the tub, with the water running and a platform for them to huddle together on as the water rises. I've never tried the tub, but the car ride has worked for me, more than once. Another trick is to smear them all with yoghurt, and by the time they finish grooming it all off one another, they will have bonded.
I think you're right, it's partly the distraction, and partly the common challenge. Or the challenge is the distraction. Or something.