Filtering Themes List

I am exploring the use of domain access and currently looking at how themes will work.

I have a theme and a number of subthemes stored in sites/default/themes. the subthemes are basically the themes I will want to apply to each subdomain.

Each subdomain currently lists all themes and subthemes that are enabled on the default domain.

Is there a way of restructuring the file system or 'assigning themes' to one or more subdomains only. This would benefit administrators of subdomains as they would not see themes that were irrelevant to them and simplify the block administration by also removing themes there.