How To Customize The Legend Icon Based On Series Appearance In WPF Chart (Sfchart)?

<Grid>
    <Grid.DataContext>
        <local:ViewModel></local:ViewModel>
    </Grid.DataContext>
    <chart:SfChart Margin="10">
        <chart:SfChart.Legend>
            <chart:ChartLegend></chart:ChartLegend>
        </chart:SfChart.Legend>
        <chart:SfChart.PrimaryAxis>
            <chart:CategoryAxis  LabelFormat="MMM/dd"></chart:CategoryAxis>
        </chart:SfChart.PrimaryAxis>
        <chart:SfChart.SecondaryAxis>
            <chart:NumericalAxis ></chart:NumericalAxis>
        </chart:SfChart.SecondaryAxis>
        <chart:FastLineSeries Label="Series 1" StrokeDashArray="1,1" ItemsSource="{Binding DataCollection}" XBindingPath="Date" YBindingPath="Value">
            <chart:FastLineSeries.LegendIconTemplate>
                <DataTemplate >
                    <Polyline Points="0,8,25,8" Stroke="{Binding Interior}" StrokeThickness="{Binding StrokeThickness}" StrokeDashArray="1,1"/>
                </DataTemplate>
            </chart:FastLineSeries.LegendIconTemplate>
        </chart:FastLineSeries>
    </chart:SfChart>
</Grid>

public class Data
{
    public Data(DateTime date, double value)
    {
        Date = date;
        Value = value;
    }

    public DateTime Date
    {
        get;
        set;
    }

    public double Value
    {
        get;
        set;
    }
}

public class ViewModel
{
    public int DataCount = 100;

    private Random randomNumber;

    public ObservableCollection<Data> DataCollection { get; set; }

    public ViewModel()
    {
        randomNumber = new Random();
        DataCollection = GenerateData();
    }

    public ObservableCollection<Data> GenerateData()
    {
        ObservableCollection<Data> datas = new ObservableCollection<Data>();

        DateTime date = new DateTime(2000, 1, 1);
        double value = 100;
        for (int i = 0; i < this.DataCount; i++)
        {
            datas.Add(new Data(date, value));
            date = date.Add(TimeSpan.FromDays(5));

            if (randomNumber.NextDouble() > .5)
            {
                value += randomNumber.NextDouble();
            }
            else
            {
                value -= randomNumber.NextDouble();
            }
        }

        return datas;
    }
}