I've found the answer (not explicitly) in the documentation: http://www.isc.org/wp-content/uploads/2014/08/DHCP-4.3.1-Distribution-Documentation-Aug-4-14.pdf , page 22.
There we can see how parameters can be declared (not only "hardware ethernet" or "fixed-address", as we have been always been doing) and figured out that the string needed for this option to work is option routers 10.0.0.2;
So finally, this is the complete answer:
host MyClient {
hardware ethernet d8:b6:b7:40:76:12;
fixed-address 10.0.0.200;
option routers 10.0.0.2;
}