Ouch!
I don't know how Casanova did it, but I'm guessing half a cup of lemon juice on mucous membrane would be kinda painful. I see it more as aversion therapy to control you urges! There's lots of stuff that would kill HIV, for example bleach, but you might not want to put it in your body.
Hopefully they can isolate the relevant chemical and make it work within a gentler lube.