Comment 13 for bug 1211892

I could finally found a solution. I hope it works for you too.
Also, I don't use neither udev, eudev nor systemd and I don't use a conventional Gentoo environment. But it worth trying.

Packages used for the test,

x11-misc/lightdm-1.7.9::local USE="gtk introspection qt4 -kde (-razor)"
sys-auth/consolekit-0.4.6 USE="debug doc pam policykit -acl (-selinux) {-test}"

: lightdm since x11-misc/lightdm-1.7.9 needs a valid allocated tty to work on.
: most often /dev/tty7 is used for X.
: run consolekit daemon before lightdm otherwise dbus will run it on tty0 and
: will lock the tty7 until you manually kill consolekit daemon.

: /usr/sbin/console-kit-daemon --no-daemon --debug
: openvt -c 7 -- /usr/sbin/lightdm
: option -f isn't necessary in that case.
: verify if the panel has valid menus.
: open a user session in lightdm manager, run ck-list-sessions in the session
: 'display-device' should have /dev/tty7 as value this time.
:
: /usr/bin/ck-list-sessions
:
: Session2:
: unix-user = '1984'
: realname = 'User iGentoo'
: seat = 'Seat1'
: session-type = ''
: active = TRUE
: x11-display = ':0'
: x11-display-device = ':0'
: display-device = '/dev/tty7'
: remote-host-name = ''
: is-local = TRUE
: on-since = '2013-08-13T22:46:02.560669Z'
: login-session-id = '1'
: -----------------------------------------------------------------------------