Damn. I thought that prompting was for the other materia they pointed out earlier in which I got. I swear when Barret said that I really doubled back and saw no way to even physically get to the fan... I also swear I tried going back to the church at every opportunity and was prevented, and then are physically unable to... oh well, end game chapter selection time I guess! I feel better knowing it's my own incompetence rather than bad game design.