I have resisted weighing in on this topic, since I felt that my points were pretty well made on the previous threads. But what the hell – it’s not as if I have free will in the matter. 
1) An omniscient being does not possess free will
Consider an ordinary person who happens to view time in the extra-dimensional manner that cmkeller and others have suggested. That person has prior knowledge of his own actions. That person can make no action that contradicts their foreknowledge or else that foreknowledge is not perfect (they are not omniscient).
2) A being may possess omniscience of an external environment without consequences to either his own free will or the free will of those in said environment
Assume that I have perfect knowledge of everything that did/is/ever will happen in an alternative universe. I have no way to affect said universe. I do not possess omniscience in regard of my own universe. There are no consequences to my own free will, since I have no special knowledge in this world. I have no means of ever intruding my knowledge into the alternate world; therefore that knowledge can have no possible affect on the inhabitants of that world. The fact that I, operating in a different spacetime, know all events in their spacetime has no consequences on their free will.
It is not correct to speak of foreknowledge in this case, because my spacetime is fully distinct from theirs. It is no more correct to say that I know their actions before they make them than it is to say that I know all of their choices after they make them. I have no projection into their time.
3) A being with omniscience in respect to an external environment may not act in that environment without consequences to free will.
a: Free will of the omniscient being.
I have full knowledge of Bizarro world. I have the ability to act in Bizarro world. In the instant I achieve my omniscience of Bizarro world, I lose all free will with respect to my actions in Bizarro world. In this case, it is the causality of my own spacetime that is the restrictive element. When I achieve omniscience, I know for a fact what actions I will take with respect to Bizarro world. I have no ability to change the decisions that lead/led to those actions. I have no free will with respect to those actions.
An interesting corollary to this is that those actions that I take in Bizarro world are necessarily devoid of intent. The ability to express intent through action is dependent upon the ability to choose between courses. I have no ability to not act as my omniscience tells me I have/will. Therefore those actions are devoid of intent on my part.
b: free will of the Bizarro folk
The omniscient being has acted within Bizarro world. If that action is devoid of informational content, then the free will of the Bizarros is not affected. This reduces to the case in which an omniscient being cannot act in Bizarro world, since no information about the omniscience or the events of Bizarro spacetime has entered the Bizarro world.
If the actions have informational content, then free will no longer exists for any choice that might affect the outcome of events for which knowledge has been introduced in Bizarro spacetime. No choice is available to any being which would contradict the knowledge that now exists within the Bizarro universe. Whether the beings in question are aware of the information is irrelevant – the knowledge has been introduced into Bizarro spacetime and all “future” events in that spacetime are now constrained to follow the course of the omniscient knowledge.
4) The omniscience has the ability to fully alter the course of the universe of which he has knowledge
In this case, I can not only know all events of Bizarro world, but I can choose whether to act or not to act. I maintain my free will with respect to Bizarro world. The Bizarros have no free will. Consider this chain of events (seen in my spacetime).
I have full knowledge of Bizarro world.
I choose to act in Bizarro world.
The history of Bizarro world is changed by my action. The “omniscience” I possessed before acting is no longer valid; things have changed.
I now possess full knowledge of the changed Bizarro world.
I necessarily have the ability to alter my actions again, since I have just demonstrated that the entire history of Bizarro world is malleable to my actions.
I am now infinitely able to adjust my actions in Bizarro world. After every choice, I will have perfect knowledge of the consequences of my action. I can change those actions if I so wish.
The full course of Bizarro history, down to the most minute detail, is now entirely dependent upon my choice of actions.
The inhabitants of Bizarro world have no free will – the course of their lives is entirely dependent upon my choices.
Even if I choose never to act – returning the Bizarro universe to the state that it would have had if I had no ability to affect its history – the Bizarros have no free will. My choice has fully defined the scope of their existence.