Help Needed with Default Theme Issue

This isn't exactly related the the plugin, but I do need some help with a default theme mess I've gotten myself into.

Prior to activating the Default Blogs Template plugin – which works great, thank you very much – I had been setting the default theme for all blogs by renaming the twentyten folder and then naming my default theme's folder twentyten. Then came twentyeleven and I finally got around to implementing the Default Blogs Template.

My problem now is that many existing blogs throw the blank white page of doom with an Appearance notice that the "theme is broken". Easily fixed, but members freak out thinking their blog is gone. The other issue is that other existing non-supporter blogs are now using the Twenty Eleven theme, which we have enabled only for Supporters.

So my question: Is there any way to easily determine which blogs are using what themes without looking at them all (2700+) individually? Perhaps via PHP MyAdmin? Any way to identify which blogs are using twentyten? This would at least help me narrow down which blogs I need to fix.

Thanks.

NOTE TO ALL: Consider this a strong recommendation for using the Default Blogs Template or Default Theme plugin rather than renaming your default theme folder! :-\