Pay It Forward-I think this is a unique way of expressing gratitude where one kind act or thank you sets off other people to say thank you or they go and do something nice because someone did something nice for them. In order to express gratitude for the act that was performed for them, they do the act for someone else and it starts a chain reaction. This is a concept that you plant in your employees and let them take it and make it their own so that they have little chain reactions all over the place.
Rachel’s Challenge talks about a chain reaction and they can make it tailored to corporate environments. Maybe bring in a speaker like this to inspire gratitude and kindness (http://rachelschallenge.org/programs/corporate)