Instead of a charity doing a bike-a-thon, walk-a-thon, jog-a-thon, etc. how about a suck-a-thon? Volunteers go door to door offering blowjobs for donations. Instead of getting people to donate a certain amount of money per mile, it's per minute of oral.
I'll give you points for lewdness, but honestly it sounds non entertaining because women are generally too free with that sort of thing anyway.
Though i admit this post does make me think about that manga where this guy has precious stones come out of his penis whenever he orgasms.
Way back in the era of ASSTR, an author named Daphne Xu wrote two stories kinda like that.
The first was "1997 Teen Blow Job Tournament", nd the second was "1998 Teen Cunnilingus Tournament". Where the teams were made up of college students, and those who won had donations made to their respective colleges.