As you know, necessity is the mother of invention! So it’s not a problem for me to intersperse a bench press session with alternative dumbbells at home.
I lay down on my back, bend my knees and grab the Lonely Planet China with one hand and the Lonely Planet Japan with the other. They are almost the same size and so I can at least dream a bit about oriental countries while working out. I hold them straight over the elbows which touch the floor. Now I lift the books vertically up and together over the chest and then I lower them slowly.
Of course in this way the chest muscles, the deltoid and the triceps are not really worked out so much like with heavy weights, but with a lot of repetitions and a conscious tension of them they’ll stay in a good shape.