Since the Pontifical Academy of Life, in its statement opposing the morning after Pill, did not directly address the separate issue of being able to use hormonal therapy to derail ovulation and prevent conception completely apart from the risk of abortion, I do not believe the case is closed. What they say so far is, “No! Under no circumstances, including rape, because this is an abortifacient.” They clearly left enough room for the USCCB to make its statement, which, since it speaks for all the US bishops and they voted on it, would have been reviewed by the Vatican before publication.
Here’s a parallel question: Would it be licit to ask a rapist to wear a condom to reduce the chance of conception? No chance of abortion, there, so if that’s licit, then chemical/hormonal means ought to be just as licit.
Actually, though, since this is my professional field, I’m drafting a letter to the PAL, asking them to directly address the possibility and make a definitive statement. I have no idea if I will even get an answer, or how long an answer would take, but I’ll sure let you know if and when I get one!
(Yep, totally heroically virtuous to bear a child of rape, but I’m not at all convinced that it is a sin not to, if it can be done apart from abortion)