If that is right clicking from within the start menu, you can disable it via the following registry key :
HKEY_CURRENT_USER\Software\Stardock\Start8\Start8.ini\Start8
AllowPin = 0
That should be a REG_SZ value.
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If you mean in general explorer windows you would need to unregister the correct dll. (Start8Shell32.dll for 32 bit systems, Start8Shell64.dll on 64 bit)
From an admin command prompt you would type regsvr32 start8shell32.dll /u
Replace the 32 with 64 on a 64 bit install.