Disabling/Hiding Themes

Hi,

I know how to create new themes and make a new default theme, but how 
can I disable / hide themes so that users cannot select them from the 
theme tab and/or remove them from the theme editor?

Can't find any helpful extension points on ThemeService, etc. Maybe I 
have to create a component to go and remove any unwanted ones? Any help 
much appreciated.

Thanks,

Sean

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Dr. Sean Radford, MBBS, MSc
http://www.tacola.com/