I dont think you need to do anything to get the scart to output, you just need to put an adapter in like this that you could probably get off ebay etc.
http://www.playdeluxe.de/bilder/kabe...chalter_hq.jpg
and then use a lead that you can connect the headphones to. Its a bit of a an awkward way to do it I suppose but it probably works. You can buy these connection kits with all the necessaary cables in discount shops quite cheap.
It is usually only one of the scart sockets that has the output though and I think it is usually the main fully wired scart 1, so you will lose use of that scart for connecting equipment and have to use the other scart number 2 which probably isn't wired for RGB and slightly lower quality.