Add to Selection by Right Clicking & Union

I'm trying to make a code so that when optionbutton1 is checked, it allows you to right click to select a cell, then right click on a different cell and select that cell as well as the previous cell, etc. Here's What I have so far.

Private Sub Worksheet_BeforeRightClick(ByVal Target As Range, Cancel As Boolean)
Dim S As Range

If UserForm3.OptionButton1 = True Then
Cancel = True

If S Is Nothing Then
Set S = Selection
End If

Application.Union(S, Target).Select
End If
End Sub