How can I split bibliography with unique references only in the second bibliography?

Question

I would like to split a bibliography such that all references up to a point are listed in the first bibliography and all references that are listed from that point and are not listed in the previous bibliography be listed in the second bibliography. I have gone through many of the questions here but have not found a sufficient answer that I understood. In my series of attempts, I've come up with:

\documentclass[a4paper]{article}

\usepackage[style=nature,backend=bibtex,defernumbers=true]{biblatex}

\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@article{refAOnly,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
  journal={My Journal},
}
@article{refBOnly,
  author = {Buthor, B.},
  year = {2002},
  title = {Blpha},
  journal = {My Journal},
}
@article{jointRef,
  author = {Cuthor, C.},
  year = {3003},
  title = {Gamma},
  journal={My Journal},
}
\end{filecontents*}

\addbibresource{\jobname.bib}

\begin{document}

\section{Main text}
%\begin{refsection}
%\input{textA}
This is section A. This represents the main body of the text.
Here I cite a unique reference \cite{refAOnly} as 
well as a joint reference \cite{jointRef}.

% here I would like to see refAOnly and jointRef listed
\printbibliography

%\end{refsection}

\vspace{10mm} 

\section{Online only}
%\begin{refsection}
%\input{textB}
This is section B. This represents an appendix.
Here I cite a unique reference \cite{refBOnly} as 
well as a joint reference \cite{jointRef}.

% here I would like to see refBOnly listed with the number 3
\printbibliography
%\end{refsection}

\end{document}

As written, this gives me two full bibliographies. Using refsection doesn't work, as jointRef appears in both bibliographies. I don't want to go through (and change) my bib file as it's used in multiple tex files. I would prefer not to use biber, as that involves switching settings in the environment on multiple computers and back again for other projects, but will resort to it if need be (assuming it helps).

Is there a simple (haha) way to achieve this?