How to query an external content FTS4 table but return additional columns from the original content table

I am creating an FTS4 external content table in SQLite like this:

CREATE TABLE t2(id INTEGER PRIMARY KEY, col_a, col_b, col_text);
CREATE VIRTUAL TABLE fts_table USING fts4(content="t2", col_text);

I'm using an external content table so that I don't need to store duplicate values of col_text in fts_table. I'm only indexing col_text because col_a and col_b don't need to be indexed.

However, when I do a query of fts_table like this

SELECT * FROM fts_table WHERE fts_table MATCH 'something';

I don't have access to col_a and col_b from the content table t2. How do return all these columns (col_a, col_b, col_text) from a single FTS query?