I don't have much reasoning to back it up, but I think they'll push the actual execution to a bit later in the series. I'd say episode 8. I'm guessing the events between that and the hunting accident will span at least two episodes. I picture the accident happens and the beginning of the episode and the the death hapens at the end. I figure the next episode would then have ned being imprisoned in the end, followed by the actual execution at the end of the next.

Drogo's death, and the birth of the dragons, I assume will be the end of the season.

I also picture the crowning as being the end of an episode, and it has to be at least a little past the halfway mark.

So my figures then would be

6- Crowing and hunting accident. (it seems fateful for two kings to die on the same day.)

7 - Ned imprisoned and Syrio's end

8 - Ends with the beheading

9 - Reactions and I'm guessing some extra scenes on the wall

10 - Drogo's death