Alignment of custom item symbol in beamer

Dirty hack:

\documentclass{beamer}
\begin{document}
\begin{frame}
\begin{itemize}
\item a
\item a
\item[$\Rightarrow$\hskip-0.15cm] a
\end{itemize}
\end{frame}
\end{document}

---

Not so hacky:

\documentclass{beamer}
\usepackage{calc}

\setbeamertemplate{itemize item}{%
    \makebox[\widthof{$\Rightarrow$}][c]{%
        \scriptsize\raise1.25pt\hbox{\donotcoloroutermaths$\blacktriangleright$}%
        \hfill%
    }%
}

\begin{document}
\begin{frame}
\begin{itemize}
\item a
\item a
\item[$\Rightarrow$] a
\end{itemize}
\end{frame}
\end{document}

What about this solution?

\documentclass{beamer}
\usepackage{amssymb}

\begin{document}
\begin{frame}
\begin{itemize}
\item[\usebeamertemplate{itemize item}\hspace{4.6pt}] a
\item[\usebeamertemplate{itemize item}\hspace{4.6pt}] a
\item[\(\Rightarrow\)] a
\end{itemize}
\end{frame}
\end{document}