In theory it is possible using tracks like my 3x3x5 concept
but I do not think it will be stable. The cubies are just to small.
I gues the 4x4x6 is the one that could be stable, because you only needs hooks/tracks for the oustide cubies. I assme Tony used the concept of the 2x2x4 fro the outside cubies combined with the 2x2x6 for the center cubies. But I think tracks will make the 4x4x6 more stable as the hooks he probably used.
For the 5x5x5 I think it is not possible to use the inside center as axle, you need a little buildup track/hook for this.
So yes I think it can be done on paper, but what I have in mind as solution will not
I also think you could extend Tony's 2x2x6 to a 2x2x8, but this require a hook that goes to three layers, hence it will be unstable.