[OS X TeX] Heights other than "low","middle", "high" in the variations environment

[ewan.Delanoy at math.unicaen.fr]

      Hello all,

  I have a problem with the variations environment because
there is no middle heights between "low"(\l), "medium" (\m)
and "high" (\h) in it, so I can't display more than one value on
an upwards arrow. The example below (which produces
an unsatisfactory output) illustrates my problem.

  I guess that it's impossible to do that with the variations package alone.
Does anyone know about a way to fix this ?

                              TIA,

                                   Ewan

\documentclass{article}
\usepackage{variations}
\usepackage{amssymb}

\begin{document}
\noindent \makebox[\textwidth][c]{
\begin{variations}
x        & -\infty &     & -\frac{1}{2}  &    &0 & &  1& &\pI\\
\filet\filet
f'(x)     &     & -~~ & \z & ~~+ &  \l & ~~+ & \l& ~~+& & \\
\filet
%------------------------------------------------------
\m{f(x)}  & \h\pI   & \d &  -\frac{1}{4}& \cb & \m{0}&\ch & \h{1}&\ch
&\h\pI \\
\end{variations}
}
\end{document}