\documentclass[draft]{article}

\def\fixcatcode#1{#1}
\begingroup
\catcode`\ =13
\expandafter\endgroup
\fixcatcode{%
\newenvironment{countwords}{
\endlinechar=32
\catcode`\ =13
\let \countspace
}}{%
\par
There are \thewords\ words.
}

\makeatletter
\@expandtwoargs\in@{,draft,}{,\@classoptionslist,}
\ifin@
\def\countspace{\shownumbers\ }
\else
\def\countspace{\ }
\fi
\makeatother

\def\shownumbers{%
以下略