1) A (seemingly) beautiful fiend seeks to seduce the lonely and introverted gay child of a noble or other powerful figure. Family rejection is only likely to make the fiend's hold stronger.
2) A famed band of mercenary adventurers is actually made up of male couples who, like the Sacred Band of Thebes, fight fiercely so as not to shame themselves before their beloved.
3) Girdle of opposite sex? Helm of opposite alignment? How about the Item of Opposite Orientation? For that matter, what about a secret group that has turned the Girdle of Opposite Sex into a blessing rather than a curse, using it to help would-be transsexuals to achieve new lives?
4) A particular god likes to woo handsome men, and doesn't take kindly to rejection (several of the Greek gods work well for this). When he chooses an attractive heterosexual, how does the unwilling paramour say no?
5) Certain sorcerous bloodlines seem to produce more gay offspring than others (probably making them somewhat rarer as well). Is there a link between homosexuality and magical talent? (All those bards have to be coming from somewhere...)
6) A young street hustler has captured the heart of an influential man who must conceal their relationship, but who will hear nothing harsh said about his beloved, even as the conniving hustler plots to sell his lover out to his enemies.
7) A particular shrine or grove where a same-sex couple was murdered long ago is a haven for gay people seeking shelter and aid, but the vengeful ghosts destroy anyone else who violates their rest.
8) The vampire preying on local woman is not, in fact, the dashing and darkly mysterious nobleman visiting the area, but a woman in his entourage who holds the nobleman in her thrall (and uses him as her cover).