If you don't mind using luatex (ConTeXt MkIV), you can do the following:
%\setupframedtext [align=hanging]
\definefontfeature [default] [default]
[
%protrusion=quality, % partial protrusion
protrusion=pure, % full protrusion
]
\setupalign [hanging]
\showframe
\starttext
\input knuth
\stoptext

For \framed and framedtext protrusion is not enabled by default. You have to set that explicitly (see commented first line). There are several values for the protrusion key:
pure - full protrusion of only selected punctuation
punctuation - partial protrusion of punctuation and some asymmetrical letters
alpha - variable correction of character widths
quality - combination of punctuation and alpha
See ConTeXt wiki - Protrusion