Two digit sectioning in memoir class

Question

I would like to have the first 1-9 numbered heading from chapter to subsubsections be two digits.

So instead of:
1 Chapter One
1.1 Section One
1.1.1 Subsection One
1.1.1.1 Subsubsection One

I would like:
01 Chapter One
01.01 Section One
01.01.01 Subsection One
01.01.01.01 Subsubsection One

After the first 9 they should just continue 10, 11, 12 etc. without a zero in front.

Answer 1

The code of memoir contains

\renewcommand*{\thechapter}{\@arabic\c@chapter}
\renewcommand*{\thesection}{\thechapter.\@arabic\c@section}
\renewcommand*{\thesubsection}{%
              \thesection.\@arabic\c@subsection}
\renewcommand*{\thesubsubsection}{%
              \thesubsection.\@arabic\c@subsubsection}

so you have to replace every \@arabic... by \two@digits...

\documentclass{memoir}
\setcounter{secnumdepth}{3}
\makeatletter
\renewcommand{\thechapter}{\two@digits\c@chapter}
\renewcommand{\thesection}{\thechapter.\two@digits\c@section}
\renewcommand{\thesubsection}{%
              \thesection.\two@digits\c@subsection}
\renewcommand{\thesubsubsection}{%
              \thesubsection.\two@digits\c@subsubsection}
\makeatother
\begin{document}
\chapter{Foo}
\section{Bar}
\subsection{Baz}
\subsubsection{Bla}
\end{document}