SQL Server Filetable document properties
It looks like (at this time) the best you are going to be able to do is use the keywords on the property, join them up to the doc and cross your fingers it is enough.

SELECT
    keyword,
    display_term,
    column_id, document_id, property_id
FROM sys.dm_fts_index_keywords_by_property
(
    DB_ID('FileTableDB'), 
    OBJECT_ID('FileTableTb')
);


MSDN on that DMV - http://msdn.microsoft.com/en-us/library/ee677646.aspx

Here is a discussion with Bob Beauchemin and I on the topic:
https://twitter.com/bobbeauch/status/275101491084292096

Bob told me about the DMV mentioned above and pretty much confirmed that it is the most likely way. 

Here is the Connect ticket Bob created for this topic:
https://connect.microsoft.com/SQLServer/feedback/details/773212/provide-complete-fts-property-values-in-a-dmv-side-table

We also go on to talk about how it might be better to have a preprocessor of sorts to pull the meta info out, store it, (not sure if you normalize format of your docs or not), and then reprocess if modified. Bob suggests perhaps being able to pull this off with a SQLCLR trigger/proc which would be a rather clever solution and get your hands all kinds of dirty.