After a little research on ehcache we found that 'net.sf.ehcache.constructs.blocking.UpdatingSelfPopulatingCache' is the best match for our requirement.
I have followed suggestions given in the forum post (https://sourceforge.net/forum/message.php?msg_id=7382649) and realized that I can only replace the decorator cache with the actual ehcache with the help of a helper method on the CacheManager programmatically.
The question I wanted to ask is that using ehcache.xml file I was able to describe all the Ehcaches i wanted to use in my system. I feel its intuitive to declare the ehcache decorators as well in the XML itself so that I can completely centralize all my configuration at one place itself. i.e. ehcache XML. Is there a way we can add configuration for a decorator in the ehcache.xml itself ?