Here is a method using Reflection to achieve this.
[ DllImport( "user32.dll" ) ]
private extern static int SendMessage( IntPtr hwnd, uint msg,
int wParam, int lParam);
object o = typeof( ToolTip ).InvokeMember( "Handle",
BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.GetProperty,
null, myToolTip, null );
IntPtr hwnd = (IntPtr) o;
SendMessage( hwnd, 0x0418, 0, 300 );
Rhett Gong