I quite like what Gilles did herehere, using something like this1 to indicate this.
1 I'm open to suggestions.
In this case, for me it would be quite acceptable for someone to step in, and edit directly. That way I'd be notified of the edit (I believe). The only thing is that nobody else would benefit from this little nugget of wisdom. Maybe that's not a big deal?
Of course, ideally we could agree on a convention which would obviate the need for the actual footnote, and just have something like this#.