Nobody has replied because it's a forum that does not guarantee you'll get an answer.
As for your problem, the requested functionality is performed with the help of the AutoResizeCols property.
The help topic for this property contains an example of what you need:
for(int myColIndex = 0; myColIndex < iGrid1.Cols.Count-1; myColIndex++)
iGrid1.Cols[myColIndex].AllowSizing = false;
iGrid1.Cols[iGrid1.Cols.Count-1].AllowSizing = true;
iGrid1.AutoResizeCols = true;
But I'd recommend that you also read the description of the AutoResizeCols property to understand how this system works in iGrid.