My view is that at times God limits himself, as when he wrestled Jacob and Jacob prevailed. I don't know how this could be understood any other way than God limited his strength and power in this specific incidence. And if God can limit his power for whatever purpose he chooses, why couldn't he also limit his omniscience in some circumstances for his own purpose? Thus, God would be sincere when he said, "Now I know" to Abraham.
God limiting his use, not the actual attribute. God still had the power over Jacob, but limited the use of it. It's like when a Dad allows his son to beat him in a arm wrestling match. The Dad doesn't remove his power, just doesn't use it. The "now I know" wasn't that God didn't have the knowledge that the action would take place(God is eternal and is omniscient) but that God now knew Abraham would obey because Abraham had now physically demonstrated. Before, Abraham hadn't demonstrated this act. We have to be careful not to read too much into something.