The better way is to define you own list alternative.

\define[3]\ChapterList
 {\hbox
    {\hbox to .5em{#1}\hskip.5em
     \vtop{\hsize150pt\relax#2}%
     \hfil#3}}

\setuplist[chapter][alternative=command,command=\ChapterList]

I'll try that...

#1, #2, #3 being parameters which can be passed to \ChapterList, aka
\ChapterList[#1,#2,#3]. Is that correct ?

Best,
Alan