I have seen this use crop up from time to time. Here is my "AS IS" code 
I hope it may help someone else 

 Dim p As Primitive
 Dim primitivesToAdd As PrimitiveCollection = New PrimitiveCollection()
 Dim primitivesToRemove As PrimitiveCollection = New PrimitiveCollection()

 Dim xAxis As IAdvanceAxis = Nothing
 Dim yAxis As IAdvanceAxis = Nothing

 If uchartPersonChart.CompositeChart.ChartLayers.Count > 0 Then
                xAxis = CType(uchartPersonChart.CompositeChart.ChartLayers(0).ChartLayer.Grid("X"), IAdvanceAxis)
                yAxis = CType(uchartPersonChart.CompositeChart.ChartLayers(0).ChartLayer.Grid("Y"), IAdvanceAxis)
 
                If xAxis Is Nothing Or yAxis Is Nothing Then
                    Return
                End If
            End If

Dim olayers As ChartLayerCollection = uchartPersonChart.CompositeChart.ChartLayers
Dim icurrentLayerIndex As Integer = 0
Dim currentLayer As ChartLayerAppearance = olayers(icurrentLayerIndex)

   For Each p In e.SceneGraph
 
                If uchartPersonChart.CompositeChart.Legends.Count > 0 Then
                    If uchartPersonChart.CompositeChart.Legends(0).ChartLayers.Count > 0 Then
 
                        Dim lineApp As LineChartAppearance = CType(currentLayer.ChartTypeAppearance, LineChartAppearance)
                        Dim seriesCounter As Integer = 0
 
                        If Not IsNothing(p.Path) Then
 
                            If UCase(p.Path) = "LEGEND" Then
 
                                Dim oPoly As Polyline = CType(p, Polyline)
                                If (TypeOf p Is Polyline) Then
                                    oPoly = CType(p, Polyline)
 
                                    If Not oPoly Is Nothing Then
                                        ' we found a polyline in the legend.  let's replace it.
                                        ' get the centerpoint of the polyline
                                        ' get the correct icon
                                        Dim sym As Symbol = New Symbol()
                                        ' get the centerpoint of the polyline
                                        sym.point = New Point((oPoly.points(0).point.X + oPoly.points(oPoly.points.Length - 1).point.X) / 2, (oPoly.points(0).point.Y + oPoly.points(oPoly.points.Length - 1).point.Y) / 2)
                                        ' get the correct icon
                                        sym.icon = lineApp.LineAppearances(oPoly.Row).IconAppearance.Icon
                                        oPoly.PE.StrokeWidth = CInt(2.5)
                                        sym.PE = oPoly.PE
 
                                        primitivesToAdd.Add(sym)
                                        primitivesToRemove.Add(oPoly)
                                    End If
                                    seriesCounter = seriesCounter + 1
                                    If (seriesCounter >= currentLayer.Series.Count And olayers.Count > icurrentLayerIndex + 1) Then
 
                                        icurrentLayerIndex = icurrentLayerIndex + 1
                                        currentLayer = olayers(icurrentLayerIndex)
                                        If currentLayer.ChartType <> ChartType.GanttChart Then
                                            lineApp = CType(currentLayer.ChartTypeAppearance, LineChartAppearance)
                                            seriesCounter = 0
                                        End If
                                    End If
 
                                End If
                            End If
                        End If
                    End If
                End If
 
            Next p
            e.SceneGraph.AddRange(primitivesToAdd.ToArray())
            For Each p In primitivesToRemove
                e.SceneGraph.Remove(p)
            Next