I'm sure he'll gladly accept paypal.
I would like to add that maintaining contacts takes time! You must make the calls, send the emails, go to lunch, listen and respond, don't become a burden, help them with something, become friends. Maybe they have a kid who needs tutoring or need a ride somewhere. If you dine with them, find a restaurant they like and handle the details; pay your half. If they mention a play, concert or sporting event, find the tickets at a discount and a time to attend. Even if you cannot make it, give them the details on how to get the tickets cheaper. As Matt said, if they show interest in a case or topic, find some articles online and email it to them.