It is quite possible to put your feet on the box that holds the escape slide, but eventually they will slide off (it is a sloping top). It might seem like a good way to stretch out, but it doesn't really work - unfortunately (for me anyway). My strong recommendation is to avoid the A or K exit row seat.

I was happily sitting in the nearby exit aisle, and this 6' 18" tall LOTFAPPER boldly walks to the seat with the look of "I've got the best seat in the house" then realises there is no way to sit there with any comfort unless he tucked his ankles behind his ears. I heard the words "this seat sucks...".