I've managed to run the sidebar on startup by importing the reg key from a WIndows 7 x64 Installation,
this is the exported Reg
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\DesktopBackground\Shell\Gadgets]
"MUIVerb"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,\
69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,\
00,20,00,53,00,69,00,64,00,65,00,62,00,61,00,72,00,5c,00,73,00,69,00,64,00,\
65,00,62,00,61,00,72,00,2e,00,65,00,78,00,65,00,2c,00,2d,00,31,00,31,00,31,\
00,30,00,30,00,00,00
"Position"="Bottom"
"Icon"="C:\\Program Files\\Windows Sidebar\\sidebar.exe,-100"
[HKEY_CLASSES_ROOT\DesktopBackground\Shell\Gadgets\command]
@="C:\\Program Files\\Windows Sidebar\\sidebar.exe /showGadgets"
This will get the right click to show gadgets and load the sidebar at start, though I have no idea whether there is any other side effect