This is not possible yet, but we consider adding such functionality.
Can you describe your casein some more details? In particular, do you think you would get better performance with serial but unordered filter, and why.
This definitely sounds as a good argument for unordered serial stage.
At the moment, I only can promise that we will consider it, and I will let you know the decision. I think chances are good that this functionality is voted for a future release.
And since TBB is open-source, you always have the option to implement it on your own and contribute to the project :)