There are three ways to become a candidate for membership in the academy: land an Oscar nomination; apply and receive a recommendation from two members of a branch; or earn an endorsement from the branchs membership committee or the academy staff.
The membership committees then vote on the candidates and those who get a majority are invited to join.
(If the academy wanted to, they could endorse people like Pariah director Dee Reeseven though shes never been nominated for an Oscar and has only directed one filmher work has been honored at dozens of film festivals, awards ceremonies and has been financially successful.)
The present Academy members could endorse and promote the Black filmmakers who are already working in the industry, there would be more visibility and promotion in the Academy and also in the industry if the will was there to do so.
Hollywood's attitude toward Black filmmaking also contribute to the lopsided racial bias:
http://www.nytimes.com/2009/01/11/movies/11seym.html?pagewanted=all
Momentum for African-American cinema, it would seem, has been curtailed or at least stalled in part by studio executives preconceptions that black films are niche product with limited appeal.
Pariah's director Dee Ree's on trying to get her film made:
http://www.huffingtonpost.com/2012/01/06/dee-rees-pariah-hollywood-race-problem-black-actors_n_1190478.html
Dee Rees, the director of "Pariah," a semi-autobiographical coming-of-age story that focuses on a black lesbian's experiences coming out in New York City, knows the story too well. In an interview with Colorlines, the writer-director said those very words ("black," "lesbian," "coming of age"

were often enough to immediately stop film studios and backers from participating.
"We'd go to pitch meetings and the moment we said 'black, lesbian, coming of age,' they would turn around, validate our parking and hand us a bottle of water," she confessed in the interview.