this is quite a simple thing to do. Buy yourself some 1 3/4" baton about and inch thick. I usually match the length of the sill (normally a good 4 inches out past the window edge) I usually fix the baton half way between the window aperture and the ceiling. You'll need some fast grab adhesive, some screws and 7mm wall plugs (if going into masonry) and a 7mm masonry drill bit. Mark out the centre of the baton and the central position on the wall. I normally drill through the baton with the 7mm masonry bit (trust me) and then through the wall deep enough to accept the wall plug but dont insert the plug. now its time to smear that adhesive to the rear of the baton. a good bead swirled up and down the entire length. Now screw a 3 1/2" screw half way into a rawl plug (7mm brown type) and insert this into the front of the baton, tap it through with a hammer until most of the way through. Offer the baton up to the wall lining up the hole with the protruding plug. Press to the wall as straight as possible using a spirit level or tape measure. now tap the screw complete with plug into the hole and tighten. Now you can use the 7mm masonry bit to drill through the baton and into the wall, inserting the rawl plugs by screwing the screws half way and hitting through the baton into the wall and tightening. wipe off excess adhesive and if you're as fussy as I am... go round the edge with builders caulk and use the caulk tool to get rid of the excess and leave a professional finish. I'd recommend leaving it for 24hrs for the adhesive to set (I use instant grab no nails) obviously at this stage its ok to paint / stain / varnish but remember the caulk shall be wet for around half an hour. Hope this helps
Steve the Odd Jobber, December 2009