I can offer no solution to the core question of mounting the iPads, but I have found that the
Griffin Airstrap is a uniquely practical addition to a handheld iPad - I've never found anything even remotely equivalent. It gives a safe one-handed grip on any edge of the tablet, and an ultra-secure ergonomic one handed option if you slip your fingers under the rear strap. And no, I'm not suggesting this as an alternative to a mounting, rather it's just a BTW!