Forget all that.. You want to take a chance on the Lao mail system with your passport? Even a top courier wouldn't be worth the risk of loosing it for me.. Think of how much fun that would be?? Especially if it turned up weeks later somewhere else and was reported found after you reported it lost in Laos with new visa's stamped into it from your home country though you haven't been there for ages..
That's my kind of luck... Not me! no way!