hi all 
today i dived into magic UV, hoping it would help solving my case.
Unfortunately it did not 
I love this addon and often use it in the simple copy-paste tools wich are… just perfect !
what i need to do is map all parts of a non planar mesh cut in squares to the same square location of a texture. Just like i explained here : Special unwrapping problem
If anyone have an idea of how to achieve this in an other way than manually, this would just be wonderfull 8-D
For the moment i managed to do it by hand:
- create a square grid on the XY plane in 3D view
- extrude it along Z
- cut my mesh with the grid mesh
- select all faces of my cut mesh
- mark all edges seam ( CTRL+E and mark seam )
- view from top ( NUM7)
- unwrap from view
- in UV editor: select all
- scale and move the whole mesh so that one of the squares match the part of the texture i need
- select and move by hand each part of the mesh to its proper location ( using UV snapping CTRL key )
It works but is damn long to achieve for large meshes cut with hundreds squares
any idea is VERY welcome 
happy blending !