Plenty enough of them in BackStreetHeroes over the years - I dunno if they're much use in practice for all the obvious reasons - but then who really uses the rear brake anyway?
RolandSandsDesign, amongst others, do parts, demo'd here on their Softtail Bomber (well you can glimpse it anyway) at about a minute in.
As it's RSD they make it look mega cool with all the lifestyle shenanigans, and in a desert with priddy gurls, and now of course I want all of these beautiful, expensive and really unpractical bikes.