That is an idea but basically there is about 1cm plaster in front of
lintel, I could chase out a slot to the lintel and then glue some wood
as you suggest. However I am then left with a choice (1cm) fix depth
which i doubt is enough or have the wood protrude from beyond the
plaster depth, lets say (2cm) which leaves me with a 3cm fix depth.
However the brackets from the rail extend the rail by a further 5cm
which in turn will push the curtains to 7 cm from the window (too far)
in my opinion.