I have a trouble cornering him too - he just walks away before we can even start a conversation.
So ... my guess is that his role in the game is not important.
A tip to try to talk to the fast farmer is to know his pattern of movement.
Be one step faster than him, and when he decides to move a step, you come in from the top, and block him.
Either this method, or stand at one spot (preferably one close to him) until he comes.