There is an airside tunnel that connects from Terminal 7 all the way to Terminal 4. And from my recent visit to LAX there was no more signage for Terminal 8. I think Terminal 8 has been absorbed into Terminal 7 by United and Continental merging. So assuming you can access Terminal 7, you'll be able to get to Terminal 4 airside. But it's a hell of a walk. In a dark, depressing, narrow underground tunnel.