A possible solution - calculate the total image length needed by adding the length of all 4 walls together. Set up a new material with the correct length.
Temporarily line up all 4 walls in a straight line in the order the image will appear. Use 'Align 3d texture' - 'Set Origin' and specify the base point as the bottom left point of the furthest left wall for each of the individual walls. It may be best to 'Set Direction' as well to ensure it works properly.
When you move and rotate the walls to the correct position they 'should' remember the origin and display correctly.