Currently, there is no property that will give you this behavior. But you can handle an event, Model.QueryColWidth and provide the colwidths dynamically there.
this.gridDataBoundGrid1.Model.QueryColWidth += new GridRowColSizeEventHandler(grid_QueryColWidth);
private void grid_QueryColWidth(object sender, GridRowColSizeEventArgs e)
{
if(e.Index == this.gridDataBoundGrid1.Model.ColCount)
{
e.Size = this.gridDataBoundGrid1.ClientSize.Width - this.gridDataBoundGrid1.Model.ColWidths.GetTotal(0, this.gridDataBoundGrid1.Model.ColCount-1);
e.Handled = true;
}
}