custom population of full text index

Is there any way to populate a full text search index without storing the backing information in the database?

I don't mean using remote-blob-storage or FILESTREAM types. The backing information is a composite of some existing columns with the text of files on a unc share, the number of files is quite large and storing them on the database is not practicable.

I need to be able to have a record like:

| col_a  | col_b |
|--------+-------|
| ccc dd | ee ff |

Then be able to search for "ccc AND ff" without having to do a search for "ccc" and "ff" separately because there is a significant performance hit when doing this with more than 2 values (we will be frequently searching for more than 10 words across ~15 columns), additionally the value of col_b might be stored in a file on the UNC share and not actually in the database at all.

The approach I am currently thinking of is to write a custom IFilter and specify a new extension so that my table for full-text searching looks like this:

id        BIGINT
extension CHAR(3)
content   VARBINARY(8)

The content would represent the BIGINT key of another table, and the IFilter would do a SQL read get the data and then return the composite value back to the FTS indexer.

The only problem I can see from this is that if my backing data is updated this table wouldn't be and as such the FTS would not re-index the new values, but this is fixed by using an update trigger on the other table.

Can anyone see a problem with this implementation? or suggest a better one?