If "ought" implies "can," though, some remarkable judgments might be vitiated, I think. In some cases, we could show that something is not obligated because it is not independently possible: e.g. it is not my duty to change the laws of physics by wishing, because no one can change such by such means. However...
One famous Catholic theologian argued that since only humans should, but since only God could, atone for the sin of the world, it is therefore possible for God to be an individual man, representative of humanity, who atoned by His actions for the sin of the world. From there it is only a few small steps to the conclusion that the man Jesus Christ was this dual-natured fellow (one premise being, "Who else but Him appears to have satisfied the relevant description?"). Of course, that a divine magnitude of power is required for redemption is no longer so deeply or widely held to be true, or even if it is, the relevant infinite might, might very well be located in the very free will of any individual sinner, and not in a deity alone.
So set all that aside, for a second, sort of, and consider this instead:
- 1. Jesus Christ did not deserve to die.
2. Not only did He not deserve to die, but due to the way He lived His life, He deserved to come back to life.
C. Therefore, there was some way for Him to come back to life.
3. The only being capable of bringing someone back to life for the sake of said person's deserving so, would be a divine being.
4. There can only be one truly divine being.
C2. Therefore, a divine being exists Who could have resurrected Christ.
Another thing I wondered in this context, though, was whether it might be true that we ought to have one "supernatural" perception of things. That is to say, it might be considered morally good, if we were to perceive one truth in a non-natural/normal way. There might be some kind of truth that we know is inaccessible to empirical investigation, some non-empirical question to be answered, that it would be morally good to have the answer to. In that case, we would be able to know at least one thing in some entirely transcendent fashion. The issue would be showing that some given question (written down in empirically-perceived language no less, though!) is one that we deserve an answer to. We might suppose, "We ought to know the ultimate truth," to be an example of such a thing, where "ultimate" means "most important," in which case we would be saying, "We ought to know what is transcendentally good (what is most important) not only by abstract reasoning but by intuition." Paradoxically enough or not, though, we would not be allowed to know such by intuition until after we knew it discursively, which is to say no one could claim to have had this intuition so as to exempt oneself from having to rationally justify one's moral stance before others.
Finally: suppose we ought to pursue moral ideals, to become morally perfect. In fact moral perfection is nothing more than to have discharged all of one's duties and satisfied all one's permissions and prohibitions, and to have gone as far beyond the call of duty as possible. To do this under threat of eternal death does not seem possible, though, in the sense that if we die having left some obligation unfulfilled, it should be possible for us to have some kind of afterlife/resurrection-state given to us, whereby we would be able to fulfill our lost obligation. As with the example of Christ's fate, it is not so clear at all that we really ought to remain conscious of our free will, after our physical body has ceased to tangibly function of itself. So as Kant says, the eternity theorem is a postulate of practical reason, not an axiom like the assertion of free will.