It's my understanding that one can't approach doubtful Sacraments even if a certain path does NOT exist ... except in danger of death, but someone can correct me if I'm wrong.
What you said agrees with Callan and McHugh's
Moral Theology:
https://www.gutenberg.org/files/35354/35354-h/35354-h.html678. We are obliged always to follow a safe course, that is, not to expose ourselves to the danger of formal sin (see 249, 258); but Tutiorism errs when it teaches that we are also obliged always to follow the safer or safest course, that is, never to expose ourselves even to the danger of material sin. There are cases, however, when we are obliged (because some law requires it) to follow a safer course, that is, not to expose ourselves or others to some great harm. Thus, we must follow the safer side in the following cases:
(a) when there is question concerning something essential for the salvation of ourselves or of others, for the law of charity forbids that any risk be taken in this supremely important matter. Example: Titus instructs the dying Caius only concerning the existence of God and of the future life. He should also instruct him about the Trinity and the Incarnation, which is the safer course, since it is more probable that an explicit faith in these two mysteries is a condition of salvation;
(b) when there is question of some great spiritual loss or gain for ourselves or others, for justice or charity forbids that we take chances in such affairs. Examples: Sempronia doubts whether she is excused from the law of abstinence, and whether she will be guilty of sin if she eats meat. Caius doubts whether attendance at a certain school will do harm to the religion of his son. Balba doubts whether she is bound to inquire about the truth of her sect. As long as their serious doubts remain, these persons should follow the safer course;
(c) when there is question of the validity or invalidity of a Sacrament, for the virtue of religion requires that the Sacraments be administered with fidelity, and be not exposed to the peril of nullity. Example: It is not lawful to consecrate matter that has probably been substantially adulterated;
(d) when there is question of some temporal good or evil to oneself or another, and one is certainly obliged to promote the former or prevent the latter. Examples: Caius suspects that a drink before him is deadly poison; Titus suspects that an object at which he is preparing to shoot is a human being. Neither may disregard his suspicion, even if its contrary is more probable, because the safer side must here be taken. The Fifth Commandment forbids one needlessly to imperil one’s own or another’s life.
679.
In emergency one may expose a Sacrament to nullity by taking a course that is less safe for the Sacrament, but safer for the subject, relying on the axiom that the Sacraments are for men, and not men for the Sacraments. Example: Titus is called to baptize the dying Caius. No water can be procured except rose water, whose sufficiency is doubtful. Titus not only may, but should, use the doubtful matter, since no other can be had.