
\unprotect
\startsetups [numberitemleft]
  \hbox to \dimexpr\getitemparameter\itemlevel \c!width - 
                    \getitemparameter\itemlevel \c!distance\relax 
   \bgroup \hfill
\stopsetups

\startsetups [numberitemright]
  \egroup
\stopsetups
\protect

\defineitemgroup
   [enumerate]

\setupitemgroup
   [enumerate]
   [each]
   [n,packed]
   [left={\setups[numberitemleft]},
    right={\setups[numberitemright]},
    stopper={.},
    width=2pc]

\starttext
\startenumerate
     \item The first item.
     \item The second item.
     \item The third item.
     \item The fourth item.
     \item The fifth item.
     \item The sixth item.
     \item The seventh item.
     \item The eighth item.
     \item The ninth item.
     \item The tenth item.
\stopenumerate
\stoptext
