Comibining UPDATE ... SET ... FROM (SELECT ...) with a JOIN

Good afternoon,

I have a question please.

In one table I store user ids and their IP addresses -

CREATE TABLE words_users (
uid SERIAL PRIMARY KEY,
ip inet NOT NULL
);

And in another table I keep 2-player games and timestamps of last moves
(NULL if a player hasn't played yet):

CREATE TABLE words_games (
gid SERIAL PRIMARY KEY,
finished timestamptz,

player1 integer REFERENCES words_users(uid) ON DELETE
CASCADE NOT NULL,
player2 integer REFERENCES words_users(uid) ON DELETE
CASCADE,

played1 timestamptz,
played2 timestamptz
);

When a user wants to start a new game, I first check if there is maybe a
new game already available - with just 1 player while the other "seat" is
vacant:

UPDATE words_games g1
SET player2 = in_uid
FROM (
SELECT gid
FROM words_games
WHERE finished IS NULL
AND player1 <> in_uid
AND played1 IS NOT NULL
AND player2 IS NULL
LIMIT 1
FOR UPDATE SKIP LOCKED
) g2
WHERE g1.gid = g2.gid
RETURNING g1.gid
INTO out_gid;

This code works great, but now I am trying to add an (obviously not solving
all cheating/proxy/etc. problems) check, that the IP addresses of both
users must be different.

Fetching "ip" in the internal SELECT statement is trivial with:

UPDATE words_games g1
SET player2 = in_uid
FROM (
SELECT g.gid, u.ip
FROM words_games g, words_users u
WHERE g.finished IS NULL
AND g.player1 <> in_uid
AND g.played1 IS NOT NULL
AND g.player2 IS NULL
ON (g.player1 = u.uid)
LIMIT 1
FOR UPDATE SKIP LOCKED
) g2
WHERE g1.gid = g2.gid
RETURNING g1.gid
INTO out_gid;

But how to fetch the "ip" column in the surrounding UPDATE statement?

Thank you
Alex