Because I often work internationally (mainly U.S. immigration), I actually have made contact with some of the airlines about becoming a miles provider for clients who engage my services. I am still in the process of accumulating information about costs and processes before jumping in to become a provider.
Unfortunately, I don't practice in the area of real estate. But, I believe many U.S. attorneys will start offering miles for those who engage their services once they see their value as potential client recruitment.
After all, the U.S. churns out nearly 60,000 law school graduates annually, and more than half the world's attorneys are located within one nation. Anything to have a competitive edge...