If you are visiting certain restaurants on a regular basis, maybe buy him a gift card for the restaurant or even just one of those visa gift cards. You can do some math for a good amount to give him. Just give it to him as a appreciation gift. Tell him he can spend it any way he wishes, but you'd love for him to spend it on you.
He can pay every time without thinking that you are the one actually contributing. At least that's how I would feel. When I was dating my wife, she wanted to contribute on our dates but I felt uncomfortable with her paying. A few gift certificates solved the problem.
Just an idea. I am sure others can come up with much better advice.