"31 per cent women, 15 per cent visible minorities, 4 per cent disabled, 1 per cent aboriginal."

I think you are assuming that there a no people from those groups that can match the abilities of the white boys. 
Where is the problem with filling 50% of the slots with whites with abilities that are ranked a '10.'  
Then stop with the whites and fill the next 31% of slots with women held to the same standards as the chosen whites, also a '10'. 
Then enough with the girls and fill 15% of the slots with equally qualified visible minorities.

Although the percentages you refer to aren't representative of the population.