I finally got round to solving my per-user chrooting issues by hacking suPHP to read the /etc/security/chroot.conf file if no global chroot is specified, allowing individual users to be chrooted.
The patch is against 0.6.3 with all the Debian patches (or perhaps it's 0.6.2-3) and is running in production at the moment, but I wouldn't really consider it ready for production use elsewhere.
Download: suphp-0.6.3-chroot.diff
"Para un proyecto que estoy realizando, por varios motivos necesitaba reducir el número de de peticiones SQL que estaba realizando."