The TrayDeskBand class is registered by EXPLORER.EXE through the COM function CoRegisterClassObject when EXPLORER creates the desktop and taskbar. In ordinary practice then, almost all Windows programs can get an instance of this class created for them by using such well-documented COM functions as CoCreateInstance, treating EXPLORER as a local server, and giving the following CLSID:

CLSID_TrayDeskBand {E6442437-6C68-4F52-2CFED267EFB9}

Though the class is not formally documented, the CLSID is defined in SHOBJIDL.IDL (and thence also in SHOBJIDL.H), which also declares the class as implementing the documented ITrayDeskBand interface.