I guess think that's where the misunderstanding is. The reason why he's thinking of doing the single route is because he believes it's not a lie. Remember he doesn't think his marriage is legal because he doesn't have a marriage certificate. As for coming back to sponsor her later he was never going to pretend they just met. He will tell them the truth they were together before he immigrated but he wasn't officially married to her. He then return to Cambodia to officially marry her and bring her back.
So here's the issue at hand, If not having a marriage certificate means your marriage is not official then if he adds his wife it means he lied on the DV entry, but if a ceremonial marriage is official then going the single route means he's lying. What we want to determine is which route is the route of honesty? He's definitely not trying to circumvent the law he's trying to figure out which route is legally not a lie.