\newcommand{\subtitle}[1]
{%
  \gdef\@subtitle{#1}
}

\newcommand{\presubtitle}[1]{\def\@bspresubtitle{#1}}
\newcommand{\postsubtitle}[1]{\def\@bspostsubtitle{#1}}

\presubtitle{\vspace{-1em}\begin{center}\Large}
\postsubtitle{\par\end{center}\vspace{1em}}

\newcommand{\@subtitle}{}
\renewcommand{\maketitlehookb} {{\@bspresubtitle \@subtitle \@bspostsubtitle}}