Should start by saying that There Is No Alternative.
They are actually pretty good boys, and like trains, so they will enter into the spirit of thing at least to start with, but it will be a long long haul for everyone.
I have just bought a double headphone socket to plug them into the ipad, which might help for some of the time (any good app recommendations by the way?), but I'd be really grateful for any other tips and ideas of how to keep them silent content and not ruin everybody else's journey.
I do see that velcro and gaffer tape may be the only certain solution, but if you can think of anything less drastic..?