Instead, companies are better off focusing on making the later parts of the pipeline less leaky. Minorities tend to leave tech at a higher rate than average due to factors the company has some control over.
They should have outreach programs in high schools, partner with schools to offer intro to coding, or even help sponsor some students for after school coding classes. Sure, these won't necessarily convert these individuals into employees. But it would be part of being a good corporate citizen even if those students end up going to other companies. So there are things they can do. They aren't completely powerless.
Here's the thing: by the time students reach high school, a lot of weeding out has already happened. I recall such a program where where they had something like 7% black students. All but one were children of wealthy Nigerian immigrants. The rest of the class was actually more Asian and White than the district.