postgres: Delete rows that has foreign key while not deleting data of the foreign key table

I have postgres database, I my application is build on using django and I used south migration to maintain the database schema. I have following scenario:

user_table has a foreign key relationship with userclickstream_stream and userclickstream_click has a foreign key relationship with user_stream_table.

I want to delete all the records in userclickstream_stream and userclickstream_click. But I don't want to delete any record in the user_table. What is the best way to accomplish this?

Here is how my user_stream_table looks like:

                                    Table "public.userclickstream_stream"
   Column    |           Type           |                              Modifiers                              
-------------+--------------------------+---------------------------------------------------------------------
 id          | integer                  | not null default nextval('userclickstream_stream_id_seq'::regclass)
 session_key | character varying(40)    | not null
 ip_address  | character varying(40)    | not null
 referrer    | text                     | 
 create_date | timestamp with time zone | not null
 last_update | timestamp with time zone | not null
 user_id     | integer                  | 
Indexes:
    "userclickstream_stream_pkey" PRIMARY KEY, btree (id)
    "userclickstream_stream_session_key_key" UNIQUE CONSTRAINT, btree (session_key)
    "userclickstream_stream_user_id" btree (user_id)
Foreign-key constraints:
    "user_id_refs_id_773d100c" FOREIGN KEY (user_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
Referenced by:
    TABLE "userclickstream_click" CONSTRAINT "stream_id_refs_id_4c08df60" FOREIGN KEY (stream_id) REFERENCES userclickstream_stream(id) DEFERRABLE INITIALLY DEFERRED

Here is how the User_click_table

                                    Table "public.userclickstream_click"
   Column    |           Type           |                             Modifiers                              
-------------+--------------------------+--------------------------------------------------------------------
 id          | integer                  | not null default nextval('userclickstream_click_id_seq'::regclass)
 stream_id   | integer                  | not null
 url         | text                     | not null
 path        | text                     | not null
 create_date | timestamp with time zone | not null
Indexes:
    "userclickstream_click_pkey" PRIMARY KEY, btree (id)
    "userclickstream_click_stream_id" btree (stream_id)
Foreign-key constraints:
    "stream_id_refs_id_4c08df60" FOREIGN KEY (stream_id) REFERENCES userclickstream_stream(id) DEFERRABLE INITIALLY DEFERRED

It would be great if there is a good SQL way to take care of this rather than going the south migration route. If not I was thinking to do following:

I was thinking simply delete the record in south migration history table and re-build the schema using south I am not really sure if thats the right way to go. But to do that I need to drop the these two tables first. I might not be able to drop the table due to the foreign key relationship.

Lets say I drop it then I might be able to do the following since south migration history table doesn't have any record of these two tables.

./manage.py schemamigration userclickstream --initial
./manage.py migrate userclickstream