For I could wish that I myself were accursed and separated from Christ for the sake of my brothers, my kin according to the flesh.
I've always understood the curse to be damnation, and the wish an understandable sentiment rather than any sort of suggestion or recommendation for himself or his readers.
It would take a monstrous god indeed to create a universe in which such an exchange -- my damnation for my brothers' salvation -- were possible. For that matter, the salvation itself would be monstrous, to be spent in the company (or at least at the pleasure) of such a god. And, I suppose, the creatures saved would be monsters also, if they could find eternal happiness in such circs.
Here are happy words: Our God is not that way, our universe is not that way, our salvation is not that way, and we are not that way.
Not so happy: we do, I think, tend toward conceiving all these things in those ways.
But we are saved by the New Covenant, not the New Haggle. We are judged, not by weighing our good deeds against our sins, but by weighing Christ's sacrifice against our sins. Eternal life is to know the only true God, not unending enjoyment of earthly pleasures.
You could certainly say He was cursed, but the curse clearly wasn't damnation. And separation from the Father is impossible for the Son, so however you want to think about Holy Saturday, you shouldn't imagine the soul of Jesus helpless and alone in Sheol as the souls of even the just were before the Harrowing. When Jesus said, "No one has greater love than this, to lay down one's life for one's friends," He was of course speaking of laying down one's earthly life, not of laying down one's eternal life.
For that matter, it's not clear that St. Paul was referring, even in hyperbole, to his own damnation. A curse whose punishment is separation from Christ -- which, for St. Paul, would be separation from what he desired most -- need not be permanent to be a most dire curse. There are many examples of saints who could be said to have been accursed and separated from Christ during the dark nights of their lives, who thereby gained graces leading to their own salvation, and it seems of many others as well.