Oh, no, he's got it partially wrong. "The cleric must take a standard action to give mental orders to a commanded undead" is true, but there's no clause that he has to keep commanding it constantly. Typically the rebuker will give standing orders that last indefinitely, and only change them when they become inappropriate to the situation. "Attack every living creature which isn't me while remaining within 60 feet of me" for an example that should probably work with skeletons. For an undead that isn't mindless, you could give him a much more complicated, or more vague, standing order. "Travel with me, protect me from harm, and assist in all my endeavors, to the best of your abilities according to your own judgment."
One standard action, then go about your business while they go about the business you've set them to do until further notice. With something smart and powerful like a lich, you probably don't want to be too much of a dick with your orders though, because if it escapes it's intelligent enough to remember and plot revenge, and resourceful enough that it might be able to carry it out effectively.
Oh thanks! That was exactly what I was looking for!
And yeah, he won the lich pretty oddly.
Cleric: "so....umm....can I attempt to rebuke it?"
Dm (evil smile): "well... You can try"
Cleric *rolls dice*
Dm : "WHAT THE F***?!?!?"
And as our Dm is pretty prideful, he let him keep it