I think in order for it to be subtext and not something HP-bashers would immediately pick up on, it would have to be something that didn't include a main character.

I don't know why this first springs to mind, but in the comic "For Better or For Worse," when a main character's friend says he's gay, I think the strip did a good job talking about several hard-to-discuss issues while not making it the centerpiece.

Hell, I wouldn't mind if Harry was outed as gay. Almost wish it was.