Give them what they want! Have your family write a letter, and get it notarized, stating that you will be living at a specific address until you have located a permanent place. Please do not discount the fact that the officer must satisfy certain requirements in your application.
Doesn't necessarily have to be a lease agreement, but something with the following would be good:
Dear NVC,
Our <relative> is relocating from Japan to the US with his wife and children. We are delighted to offer them housing at <address> until such time as they find permanent housing. This is the home where <relative> spent his childhood. They will be contributing to the residence through <paying utilities, paying rent>.
Signed,
<Loving relatives>
Don't dicker with them. Let the officer be able to check the box!!! It's Japan!
Sukie in NY