This is a difficult situation because, for whatever reason he got started, it is now an established habit and something that happens when no one is around to catch and correct him in the act. He doesn't necessarily know it's wrong, but he probably remembers that every morning his people are displeased when they come in the kitchen. Dogs can read body language and moods very well. The hard part about house soiling issues is the act of going is rewarding in itself, the reward being he feels relieved after he has gone.

I really think the best solution would be to get him a crate if he doesn't have one and crate him at night. I highly doubt he will go in his crate if he has to lay in it, and if he did I would certainly suspect a medical condition going on that could be causing it. He may have to sleep in a crate several weeks or even months to be sure to break the habit, and after this if you wanted to try it out I'd just start by leaving the crate door open. The best thing to do is set him up for success, by putting him in a situation where he pretty much cannot do the behavior that is causing a problem.

I hope this is of some help.