もうこれはあきらめるしか無いのですかね、、、

Const WM_COPYDATA As Integer = &H4A
Declare Ansi Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer
Declare Unicode Function SendMessage Lib "user32.dll" Alias "SendMessageW" (ByVal hWnd As Integer, ByVal MSG As Integer, ByVal wParam As Integer, ByRef lParam As System.IntPtr) As Integer

Sub main()
Dim sendMes As New COPYDATASTRUCT
Dim str As String = "TestAPP" + ChrW(0).ToString + "Music" + ChrW(0).ToString + "1" + ChrW(0).ToString + "{0} - {1}" + ChrW(0).ToString + "TEST" + ChrW(0).ToString + "TEST"
Dim ptr As IntPtr
sendMes.lpData = System.Runtime.InteropServices.Marshal.AllocHGlobal(System.Runtime.InteropServices.Marshal.StringToHGlobalAuto(str))
sendMes.cbData = (str.Length + 1) * 2
System.Runtime.InteropServices.Marshal.StructureToPtr(sendMes, ptr, True)
SendMessage(FindWindow("MsnMsgrUIManager", Nothing), WM_COPYDATA, Nothing, ptr)
System.Runtime.InteropServices.Marshal.FreeHGlobal(sendMes.lpData)
System.Runtime.InteropServices.Marshal.FreeHGlobal(ptr)
End Sub

Public Structure COPYDATASTRUCT
Const dwData As Integer = 1351
Public cbData As Integer
Public lpData As System.IntPtr
End Structure