In regards to the question, "What can be done to encourage people with disabilities to pursue careers in the STEM fields?"
A generally "forgotten" aspect to those with disabilities is showing those same people how those disabilities are actually an asset.
It is well known in the Arts that "one must suffer" for their art, and some of the greatest art of all time has come from this. Beethoven wrote some of the greatest music of all time as he was going deaf, for example.
Those with disabilities will often compensate by becoming incredibly competent in other areas. For example, those with autism have a great ability to concentrate.
See this article:
Bottom line, don't just try to get those with disabilities to compete with everyone else on everyone else's terms......encourage them to SELL their great assets. Show them how to market themselves. They have gold, and the rest of the world needs to know it.