Using frm As New ChangeFileDialog(sourceFile)
            Select Case DirectCast(frm.Invoke(New ShowFormHandler(AddressOf _
              ShowForm), New Object() {frm}), DialogResult)
               ' ...
            End Select
         End Using

Private Delegate function ShowFormHandler(ByVal sourceFile as String)as string
 
Private Function ShowForm(ByVal sourceFile as String) As String
    Using frm As New ChangeFileDialog(sourceFile)
        if frm.ShowDialog(pOwner) = DialogResult.OK Then
            return frm.FileName
        end if
    End Using
End Function