Start walking and have your partner walk behind you and whenever he wants he will push you hard from the back. You work to stay relaxed and moving with what is given and working to be aware of the anticipation and avoiding tension and stress. You can of course do this in a group. After everyone has had their turn advance to turning to face the person who you feel is about to push you and avoiding it by walking and turning. A group is a great way to practice this as the pushed will learn to change is location and heading in regard to more than one person and develop independence of movement and awareness out of it. Next go to practice this with only one eye open while working on keeping your alignment in a partner or group setting and keeping your breath as slow as it is comfortable to work with.
Use a stick to push as well and the benefits will be greater for all as the pushers will learn to move without aggression and keep calm.