Integrity reference and inheritance

I wanted to build the following schema :

- one "generic" document table with a column doc_id ;
- a couple of "specific" document tables inheriting from doc ;
- a table refering a document by it's id with and integrity constraint
on it.

In SQL :

CREATE TABLE doc (
doc_id serial PRIMARY KEY,
);

CREATE TABLE lexique (
) INHERITS (doc);

CREATE TABLE word_doc (
id serial PRIMARY KEY,
doc_id int4 NOT NULL CONSTRAINT word_doc_doc_id_ref REFERENCES doc ON DELETE CASCADE,
);

What I tried to do next is to insert a new "lexique" entry, and then a
bunch of "word_doc" rows refering this entry. The last part fails with
a constraint violation this is quite normal since the trigger in
backend/utils/adt/ri_triggers.c makes a "SELECT FROM ONLY".

What should I do ? Should I consider another way to do what I want,
rewrite a trigger to replace the system one ?

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