Actually, the most useful application for individual businesses in this case would be (in the event that IQ tests are good at predicting who will be a good worker) to request IQ scores as part of a job application, not to discriminate based on race

The problem is that this is currently illegal in the USA. This was in fact precisely the point of the parent comment.

this is because they're selecting from a pool of people who are qualified in the first place,

When is this ever the case in practice?