Idea :

Take the usual creepy ugly fat nerd who present himself as a girl online, and make him not creepy, show he doesn't eat much, show him in a favourable way, make him just want to be someone else online, not obsessed with watching lesbian sex. You can make him someone who doesn't like his body because of social norms, and make it obvious it is the social pressure that is the cause of his own disgust. And if he overcomes this, don't make it change is online persona's gender.