I replaced a few of the windows in our house this past year and am finally getting around to finishing the trim work on the inside (the wife is getting on my case because people are coming over for Xmas) :)

Anyway, I am not sure how I attach a stool to these type of windows. It almost looks like there is a slot for an accessory stool Anderson would sell that would fit into this slot.

My thought was remove the lower piece that the staples are holding in and then that would allow enough depth to insert a stool to anchor. Just not sure if the side pieces would then be too short, just need a thick enough stool.

Here is a picture of my windows, still need to add some sheetrock around the outside.

Here is a link that might be useful: