This question was actually answered by the Vatican II Theological Commission at one point - the answer was to consult the approved authors on dissent from the authentic Magisterium. I myself, being no theologian, own none of these "approved authors". I would suspect the answer could be found in the writings of Fr. Tanqueray or St. Liguori. The CDF Instruction on the Ecclesial Vocation of the Theologian also deals with this issue:
28. The preceding considerations have a particular application to the case of the theologian who might have serious difficulties, for reasons which appear to him wellfounded, in accepting a non-irreformable magisterial teaching.
Such a disagreement could not be justified if it were based solely upon the fact that the validity of the given teaching is not evident or upon the opinion that the opposite position would be the more probable. Nor, furthermore, would the judgment of the subjective conscience of the theologian justify it because conscience does not constitute an autonomous and exclusive authority for deciding the truth of a doctrine.
29. In any case there should never be a diminishment of that fundamental openness loyally to accept the teaching of the Magisterium as is fitting for every believer by reason of the obedience of faith. The theologian will strive then to understand this teaching in its contents, arguments, and purposes. This will mean an intense and patient reflection on his part and a readiness, if need be, to revise his own opinions and examine the objections which his colleagues might offer him.
30. If, despite a loyal effort on the theologian's part, the difficulties persist, the theologian has the duty to make known to the Magisterial authorities the problems raised by the teaching in itself, in the arguments proposed to justify it, or even in the manner in which it is presented. He should do this in an evangelical spirit and with a profound desire to resolve the difficulties. His objections could then contribute to real progress and provide a stimulus to the Magisterium to propose the teaching of the Church in greater depth and with a clearer presentation of the arguments.
In cases like these, the theologian should avoid turning to the "mass media", but have recourse to the responsible authority, for it is not by seeking to exert the pressure of public opinion that one contributes to the clarification of doctrinal issues and renders service to the truth.
31. It can also happen that at the conclusion of a serious study, undertaken with the desire to heed the Magisterium's teaching without hesitation, the theologian's difficulty remains because the arguments to the contrary seem more persuasive to him. Faced with a proposition to which he feels he cannot give his intellectual assent, the theologian nevertheless has the duty to remain open to a deeper examination of the question.
For a loyal spirit, animated by love for the Church, such a situation can certainly prove a difficult trial. It can be a call to suffer for the truth, in silence and prayer, but with the certainty, that if the truth really is at stake, it will ultimately prevail.