Answer by f01 for Setting up alternate routes to blocked sites via Wi-Fi in Mac OS X

Try adding this route to your setup:

sudo route -n add <REPLACE WITH YOUR OFFICE SUBNET eg 172.16.8.0/24> <REPLACE WITH YOUR OFFICE GATEWAY eg 172.16.8.1> -interface en0

If this will not work you can delete it. Replace the x's.

sudo route -n delete x.x.x.x/24 x.x.x.x