authorship - Author without institutional or professional affiliation

Here is the case: An author has made substantial contribution while not been related to any institutional or professional affiliation.

The question I sent to Nature:

An author has made substantial contribution while not been related
to any institutional or professional  affiliation.


Is it okay for this author to include his personal email and postal
address as his affiliation in the manuscript?

Nature answer:

Thank you for your email. At this stage, please just include the author and mention this in your cover letter so that the editor is aware of the situation.

The question I sent to PLOS ONE:

According to your submission guidelines "Each author on the list 

must have an affiliation". However an author has made substantial     
contribution while not been related to any institutional or
professional affiliation.

Is it okay to include "Independent Researcher" as an afilliation
in this case?

If not, what is the recommended Affiliation for this Author?

PLOS ONE answer:

Thank you for getting in touch and for your interest in submitting your work to PLOS ONE.

Your suggestion of recording the author as an "Independent Researcher" for their affiliation is acceptable. May I ask you to clarify in the cover letter if this co-author is self employed (i.e. charges for their advise/service) when submitting your work.

If you have any further questions, please do not hesitate to contact us again.

Any thoughts and previous experience with something like this is greatly appreciated.

Thank you!