Yes, of course, you can reflect on the Buddha, the Dhamma and the Sangha mentally. If it's going to bring you in conflict with others, it's better to bow in the mind than just bow in the body and not bow in the mind. Bowing is just a ritual so certainly you can bow in the mind.
Many times when I'm in the West there's no Buddha statue around, but I can have a mental image of the Buddha. Fortunately over here I get to see plenty of Buddha statues and the image gets imprinted quite well in my mind, so when I'm in the West, I can bring it to mind quite easily. Sometimes in an airplane I might bring the Buddha's image to mind. So yes, why don't you bring up a mental image and then bow in your mind to the mental image, understanding what that means.