That's precisely why the classical PHP model is kinda stuffed under this situation.
If you want to stick with the traditional disc-read-per-request model, I'd be interested to see if something like a blue/green code deployment could work. You'd have two separate html roots - say, with /var/www/blue being current. You deploy your new code to /var/www/green, update httpd.conf to point there, then SIGHUP apache. The next deployment would switch back from /var/www/green to /var/www/blue. That way every request sees a consistent deployment from start to end.
