The ends are just like the 2x2x2 corners, with all there possibliities , I consider this not a few position.
I assume you that you refer to a few postiotiins if the shape is 2x2x4. And you have solved one end.
Your idea is not new and is part of US patent 4,593,907
Abu-Shumays, et al. June 10, 1986
Filed: July 2, 1982
This patent also decribe "our" 2x2x4 extension, most of the 2x2x2 extension are described in this patent!
This is a picture: