The \start/\stop section alternative works nicely. Thanks!

I was trying to work on an automated solution consisting of three parts:

1) Define a new marking which processed normal section title marking

2) Check width to see if we need to apply clipping and add "..."

3) Performing clipping

Here are my unsuccessful attempts for 3:

% clips width correctly but descenders are also removed

\clip[width=3cm]{Long Title for Section Four}

% does not work with \dimexpr (expansion issue?)

\setbox0\hbox{Long Title for Section Four}
\clip[width=3cm,height=\the\dimexpr\ht0+\dp0\relax]{\box0}

% but this one works

\setbox0\hbox{Long Title for Section Four}

\clip[width=3cm,height=18pt}{\box0}