To activate ibus-mozc, please add the following into ~/.xinitrc,
~/.xsession, or ~/.kde4/env (for KDE4):

export GTK_IM_MODULE=ibus
export QT_IM_MODULE=xim
export XMODIFIERS=@im=ibus
%%PREFIX%%/bin/mozc start
ibus-daemon -r --daemonize --xim

Note that textproc/ibus-qt with IBUS option is required to
make QT_IM_MODULE=ibus work.