How do we make the applicant pool more diverse? That's easy.
Step one: improve economic forces on lower-income families, the working poor, migrant and other ethnic immigrant communities, and the most at risk of poverty, incarceration, preventable disease and unplanned pregnancy.
Step two: provide education for all those groups.
Step three: balance a new middle class through job creation combined with a return to increased domestic jobs which don't require a college degree (since nobody can afford it now), primarily industrial and manufacturing.
Step four: as a new middle class emerges, the roadblocks to a good education, freedom from incarceration, increased communication skills, and improved local ethnic-minority economies produces tech workers who have the same intellectual and cultural advantages of caucasian-american males and females. suddenly more people who are 'like us' start applying, and their skin color, family history, cultural/religious differences and accents don't seem like such a barrier anymore.
Alternate plan:
Step one: get involved in community outreach for young disadvantaged people.
Step two: invest in tech classes at community centers.
Step three: convert blighted neighborhoods into training centers, call centers, minimalist office spaces, etc.
Step four: work with local governments to increase availability of cheap public transportation.
Step five: hire local young people who are now trained in tech work to do the jobs you'd normally farm out to similarly-skilled foreign workers.