Upyu

I don't think Tohei ever did the multiple uke collapse gimmick, but the principle is still the same.

Training for a year in "structure" training certainly makes you "heavier" to the touch, simply because the body begins to understand some more fundamental concepts of balance etc.
One "instant results" trick I like to show occasionally, is where you have someone lift you up from the chest.
The first time, they're not aware of the upper center and easy to lift up.
The second time, you have them put a little bit of relaxed tension in the upper center (in the sternum) and maintain an opposed top to bottom tension (but still relaxed). They become immediately harder to lift up, because they're maintaining the upper center stability.
If you start to put in lower center/dantien usage etc, then they become even harder to lift. (basically its an easier version of tohei's unliftable body)

This directly correlates to okamoto's parlor tricks.
The overall idea is that you don't manipulate Uke themselves.
Rather since the Uke are holding you up, you and them are essentially one "unit." This means that you can access the "ground" through them and place your "jin" force whereever you want. In this case you place it in a "hole" in one Uke (best place is perpendicular to the feet), destabilizing the entire ring of Uke, causing them to collapse. To them if feels like you suddenly became heavier, but that's because their balance is completely shot without them realizing it.

The "building block" process is outlined on the website, and I think Tim Fong did a good general overview of our approach on the aikido journal website
http://www.aikidojournal.com/article?articleID=699

I say "our approach", though really its not "original" in a pure sense.
Its simply an "approach" to developing qi/jin skill.
Plenty of other CMA use similar theory/approach in developing these skills