Open Source Document Management System | OpenKM

Would it be possible to alter the search engine so that it searches for Boolean Property Groups which have the value of "false"? For instance, let's say I have old books on my OpenKM and need to have users index them (put in ISBN, authors, titles, etc.) by using a custom property group but I want to be able to search for books which have a "false" value for the field "Sorted".

Does that make sense?

I've added the bug in http://issues.openkm.com/view.php?id=2021