Generally, when I aim to put fetishes into the comic, I reason out how the characters would likely respond to such. For example, the hypnosis that Inalao used was done with horny purposes, but also done so in such a way to spark development and emotional responses from the characters.
In terms of balance, it's not really difficult at all, it's just a matter of making sure any scenario makes sense and doesn't just happen for no reason. Like any degree of writing, it all flows smoothly when there's reason behind everything.