Stick these onto the tops of the eclairs with a little confectioner's custard.
Refrigerate until needed, but do not serve too cold.
Remarks
It is not essential for the nougatine to be a rectangle exactly the size and shape of the eclair. On the contrary, the "deconstructed" look with pieces laid side by side can be attractive.
Some recipes insist that the caramel for the nougatine should be made "dry", i.e. without added water, but I don't think this is essential.