I have located the registry key which controls which global themes are shown within 'Aero Themes'. If you right-click the desktop you only get 1 global theme based on your location (United Kingdom, South Africa, United States, Canada & Australia).
There is a very simple method with which to add all the above to the 'Aero Themes' section rather than as 'Installed Themes'. Just run regedit and navigate to
an add the following string values (edit->new->string value)
(See Pic 1)
NOTE: 1 of these will already be listed in your registry, just add the 4 that aren't
Now, whenever you richt-click the desktop & Personalize, you will have the above listed themes showing as 'Aero Themes'. (See Pic 2)