*We do something called imovable posture from both standing and seiza. Just before his push lands drop your center forward and down. If you get it right they bounce off...it's kinda funny.
*Was he standing with hips facing square forward? If so as he pushes turn 90* so you are on the inside of the push (by turning your hips you extend your reach so unless he had much longer arms you should be able to reach him but remain just out of his reach). As you turn extend an open palm strike into the lower portion of the breast bone or into the shoulder joint of the pushing hand. Important to have that dropped center thing going on here too.
*Move to the outside of his pushing arm, slide forward and grab him by the throat, place your leg behind his and choke slam him backwards. Actually if you place the palm of your hand at the top of his breastbone and gently curl your fingers around his neck it looks like a choke but isn't really. It freaks people out to suddenly have a hand at their neck but you're not actually doing any harm...unless of course you want to.
*Spit in his face then kick him in the nads.
*Tell him you want to take it outside. Make sure he goes out first then lock the door and call the police.
Soooo many options, just depends on what you want to accomplish.
p.s. If you don't work from this attack in the dojo you should ask to (if asking is allowed).