@JKenP - well we can agree to disagree on your input being "useful" to this thread to date.
As I said above this a technical forum for the Calibre developers to discuss the most appropriate way to solve a problem. I'm not interested in people posting here that they have no use for a particular feature when it is so obviously an optional addition. Every few days there come up other potential uses - even yesterday when someone suggested wanting a plugin to be able to find books in their library which had won awards. Guess what an extension to the Goodreads metadata plugin to populate an awards custom column could do for them if this feature were available?
@JohnnyRocks - obviously we have come to our own solution between us via PM outside this thread but to officially answer your question anyways for the benefit of others. The correct solution to this problem appears to involve a lot more Calibre code changes than I had hoped, which means I will need to vamp some input from Kovid/Charles. Which makes it all a lot more complicated to get done. I am still keen on it, but I'm not going to take it on myself right now without help.