This idea came to me recently after browsing a branch on the Anime Addventure, but, as the title says, I'm worried about whether or not it'd be possible to use it without rendering one or more characters completely OoC.
The basic idea stems from the fact that Ranma is not sexually naive so much as he is naive in the ways of intimacy- canonically, he knows how sex works (the scene from the Happo Fire Burst story where Ranma is feeling horny, recognizes exactly what he's feeling and why he's feeling that way, is proof of that), but he is, for obvious reasons, quite in the dark when it comes to things like hugs and other such touchy-feely behavior. The fact that no one (that I know of, anyway) has ever bothered to make a story capitalizing on such an idea gave me the encouragement to start giving the idea serious thought, though I just had to come here to get some worried off my chest.
Anyway, the idea is that one of Ranma's fiancees realises that the reason Ranma keeps running off when they try to cuddle or touch or even spend quality time with him isn't that he's playing hard to get, or due to the machinations of those other girls (at least, not entirely): it's because he's so out of his depth in such a situation that he can't help but flee in fear. As they obviously can't have that, the only option is to try and educate Ranma in the 'gentle arts'... but, equally obviously, they cannot do so themselves- they may not admit that they can't really trust themselves to overstep the profesional boundary, they can admit that Ranma will be so nervous of them that it'd just make things harder, and/or that their efforts would draw the jealous fury of Ranma's other would-be brides.
So, an outsider is obviously required. The one chosen? Nabiki Tendo; skilled in the arts of dating and courtship, open to bribery no matter who her deeds hurt, and completely disinterested in wooing Ranma. Basically, the girl approaches Nabiki in secret and offers to pay her a suitably hefty sum for being Ranma's 'tutor' in the lore of intimacy.
And here's why I was worried: would any of Ranma's other suitors really be able to look at the situation logically enough to come to that sort of decision? And even if they did, would they be able to reign their jealousy in check to be able to stand having Nabiki be the one to teach Ranma that hugs and the like aren't scary? And, finally, would Nabiki really be willing to teach Ranma about *that* in exchange for money? Yes, she is greedy to the point of stupidity, but she's also kind of lazy, and definately interested in preserving her own skin (though her greed can overwhelm self-preservation instincts)...