I opened up Enterprise_PageCache_Model_Processor (visible here: http://paste2.org/s82y2p95) and tried to add the theme name to the cache URI but calling "getTheme('frontend')" (which I was doing around line 94) simply results in a Magento 404 page - even if I just try to silently log the value. Probably there's an exception or something (I haven't had time to debug).

Looking at the file's source above, is that the right approach, do you think?

Thanks.