Based on the book structure, that Daenerys scene will happen with two or three episodes left in the season. Assuming she skips an episode here or there, I don't see how they can draw out the conquest of Yunkai very long. Actually, maybe they could...
3.06 - No Dany
3.07 - Arrive at Mereen, argue about the walls.
3.08 - Host the sellswords, Daenerys reveals plan to sneak attack
3.09 - Daenerys sits in tent whining to the slave girl she got with the army, or maybe with Barristan
3.10 - Parade of liberated slaves and tribute.

If they drop her from a second episode, they can compact that even more. I guess that, or Tyrion's cliffhanger fate would make an acceptable final scene. Or maybe even Catelyn's first appearance as Lady Stoneheart.

Regarding the RW arc, I figure that would make a good climax for episode 9, leaving three episodes to fill, two if they drop Robb/Catelyn for an episode. So maybe in 3.06, they treat with the Freys about marrying Edmure, in 3.07, Robb argues with Catelyn about legitimizing Jon, announces plan of attack. In 3.08, they ride into the Twins, maybe with Gray Wind's freakout and the sinister meeting with Bolton. Then 3.09 is the massacre.

For Tyrion, they have an episode with his wedding, a couple more introducing the Dornish, a reaction to the Red Wedding and Joffrey's wedding in 3.10. The only problem there, is that Jaime's arc has moved forward a bit fast. Figure in 3.06, he has his meeting with Bolton, after that, his next event was learning of Joffrey's death. They might pad it out, and give him a reunion with Tyrion and Cersei, but who knows. There is plenty of room in the other characters' arc to draw out the story to finish the season with the weddings, and with Tyrion, it is highly unlikely that they will be able to squeeze in his trial, duel, escape and patricide, and there really isn't a good place in that sequence for a season break.

In season 4, he could break up the events in the following way:
- brooding in the dungeon, getting briefed about trial
- trial, ending in the Red Viper's offer
- trial by combat
- escape & murder of Tywin
- sea voyage
- meeting Illyrio
- meeting Griff & co
- boat trip
- reveal of Rhaegar's son
- kidnapped by Jorah
You could compress a few of those into single episode, if you are going to leave him out of one. It also gives plenty of time for Jorah to help Dany take Mereen, and then be disgraced and exiled.

For Dany, if season 3 ends with Yunkai, they could do the following:
- arrive at Mereen, duel of champions
- assassination attempt, exposure of Jorah
- taking Mereen
- settling victory stuff, exiling Jorah
- holding audience, Drogon's child kill revealed
- problems with Mereen resistance
- marriage proposal
- wedding
- siege
- pit fight, Drogon's return

If you are going to add the Quentyn Martell stuff, that can be extended and other things compressed, and of course, there are at least three sex scenes with Dany that can be scattered over seasons 3 & 4 to further pad her arc. Drogon's return seems like the best season-ending climax, aside from the ending where she decides to rule Mereen, but as with Tyrion's aSoS arc, there does not seem to be room to fit it all in this season or enough to stretch it over all of next year without including the DWD stuff.