I think if the president will start promoting bitcoin it will be definitely an effective way as president is the most influential person in a country. Many people will start to get curious what's this all about. Then bitcoin will be talk of the town and everything will just follow.
There won't be a lot of presidents that you'll hear talking about bitcoin. It would likely come from financial heads and banks. Regular peiple would benefit heavily here instead of those at the government since bitcoin is free from government's hold and manipulations