I'd second the suggestion of implementing the rule that either the table or the breakfast bar is where the food is laid out and is available. If he wants to eat, he sits down. If he gets up and leaves the table, he doesn't get to eat while he's off doing whatever. I'd also suggest having definite meal times and eating your own meal with him.

Don't make any fuss over it or even comment on it, just calmly continue with your meal. If he comes back and sits down, he can have some more. Make sure the areas he can wander off into are safe and ok for him to roam largely unsupervised while you continue to eating, keeping an ear out for any major dramas. Your attention is the biggest tool here, where if he sits and eats he gets to be with you, to talk to you and interact. If he doesn't, well, it's pretty boring. No one to talk to, no TV on or distractions. Eventually boredom, curiousity and hunger will lead him to come back to the table and sit down.

Good luck