Here's an article on Yahoo news that shows doctors are doing this.
I copied the first couple paragraphs here, or you can follow the link.
Basically, if you give the person a bone marrow transplant at the same time as the organ transplant, the person won't reject.
http://news.yahoo.com/s/ap/20080125/...VKcx.1EfCKOrgF
Doctors report transplant breakthrough
LOS ANGELES - In what's being called a major advance in organ transplants, doctors say they have developed a technique that could free many patients from having to take anti-rejection drugs for the rest of their lives.
The treatment involved weakening the patient's immune system, then giving the recipient bone marrow from the person who donated the organ. In one experiment, four of five kidney recipients were off immune-suppressing medicines up to five years later.