Race is never relevant; would be crude and rude to think it is. But please let this issue die of natural death so this does not turn into a flame thread and overshadow the original poster's question.

To the question of blocking J seats....of course you can ask for such. For CX, not only can one get a block seat but also obtain "last to release" consent from the flight controller. That way, as the other business class passengers (or op-uped) check-in, even the middle J class seats will fill-in before the blocked seat if you receive the consent. But if J is fully occupied....so goes your last to release seat