Aditya finally gave me a great solution on Stack Exchange:
One way to achieve this is to explicitly set the width of each symbol,
and align the symbol to
the right. Visually, this is give the output that you want. For example:
\definesymbol[emdash][---]
\setupitemize[1][packed,
Hello,
How can I get the output given by the following code with the itemize
environment?
\starttext
\quad---~Sed ut perspiciatis, unde omnis iste natus error sit voluptatem
accusantium doloremque laudantium, totam rem aperiam eaque ipsa, quae ab
illo inventore veritatis et quasi architecto
