Even if they split up ASOS into two seasons the non-book readers are going to be pushed pretty hard. The amount of drama in ASOS is pretty staggering:
The Red Wedding, particularly the disturbing description of Cat going insane after watching Robb die. Followed by her throat being cut.
Joffrey's assassination.
The Shaetrayal of Tyrion and his revenge against her and Tywin.
Jaime's hand getting chopped off.
Selmy joining up with Dany and her telling Jorah to GTFO.
Lysa Arryn getting a free ride through the Moon Door.
The Hound killing Dondarrion and his resurrection.
Mountain vs. Viper.
The battle at the Wall, the death of Ygritte.
There are going to be meltdowns.
Oh and the most important person of all:
STRONG BELWAS
Here's how I figure they may do it:
(I'm assuming there will be 10 episodes)
Season 3:
-Arya meets up with the Brotherhood early on, spending most of the season with them, before Beric and the Hound duel and Beric is resurrected in episode 6, she'd leave in episode 8, only to be captured by the Hound.
-Jon Snow meets up with Mance in the first episode, and then spends the majority of the season just making his way towards the wall, getting his loyalty tested in various ways, and falling for Ygritte. His story would end with their scaling of the wall, leaving most of his action sequences to season 4. Have them come across the Fist of the First Men around Episode 3 or 4, and cut to Sam and the retreat to Crastor's Keep. The coup could happen about midway through the season, and then have Sam meet Coldhands in the finale to fan the flames of speculation.
-Jaime's hand gets chopped in episode 8 he sends his regards to Robb Stark, and then he and Brienne arrive in King's Landing in the finale.
-Dany makes the decision to head to Astapor in the first episode, and I suppose the first few episodes will be like season 2, with her not playing a large part, as she'll be on the ship heading towards Pentos/Astapor. Her taking of Astapor would happen in the finale, since it seems like the show's getting into a theme of ending each season with an emphasis on her dragons.
-I can see there being a lot more focus on Robb in season 3 in order to get the audience invested in him. Ideally, his war against the Lannisters would still be going in his favor, so that everyone already knows he is going to lose by the Red Wedding. There needs to be that hope that he can still win to make the RW all the more crushing. Episode 9 will probably focus on the Red Wedding, as the penultimate episode usually contains the most pivotal moment of the season. The only thing I'm worried about is how they'll mask the surprise of the RW, while building anticipation for the episode. It was easy this year since everyone knew they were building up to Blackwater, whereas they can't make the Tully-Frey wedding the center of promotion for the episode without people starting to think.
-Davos and Stannis's story in season 3 would mainly concern their recovery from the defeat, and Davos' imprisonment. I suppose they could focus on him plotting against Melisandre early on, and end the season with his release and being instated as as Hand of the King.
-In King's landing, they would include Tywin taking over, Joffrey's continued prickery, and Sansa's marriage to Tyrion.
Season 4:
-Arya would continue with the Hound, hopefully building up audience sympathy for him, before he dies about midway through. Arya's story ends with her going to Braavos.
-Most of Jon Snow's important storylines would be moved to this season, as he would be the main character of the season. This season would have the attack on Castle Black early on, the penultimate episode would focus on the main battle and Stannis arriving, and the finale would have him being elected Lord Commander.
-Joffrey's wedding would take place and Tyrion would be imprisoned. Littlefinger and Sansa would escape in the same episode. The Oberyn-Mountain duel would take place near the end, and would coincide with Littlefinger admitting his part in Joffrey's murder to Sansa, and Lysa's reveal about Jon Arryn's death, before her own.
-Dany's storyline would basically be the same as the books, in that she goes about conquering Slavers bay.
-Stannis and Davos' storyline would initially concern their poor position, transition to Edric Storm, before finally leading to their aiding the Night's Watch.
I think they can move Tyrion's escape and murder of Shae and Tywin to Season 5, just to add some more action to that season to make sure there's not too much of a letdown.