Eu entendi. Existe um utilitário chamado xbkeys para configurar opções de acessibilidade para o xorg.
Do manual do xkbset ($ xkbset man):
To switch sticky keys on or off, and optionally set or reset:
() two keys pressed at the same time stops sticky keys;
() a modifier pressed twice will be locked:
[-]{sticky|st} [[-]twokey|[-]latchlock]...
Eu corri isto:
$ xkbset sticky -twokey -latchlock
Esse comando pode ir em .xinitrc
# turn on stickykeys. don't let two keys pressed at the same time disable it.
# don't turn on "latch lock", ie pressing a modifier key twice "locks" it on.
xkbset accessx sticky -twokey -latchlock
# don't expire these settings. (run xkbset q exp for details.)
xkbset exp 1 =accessx =sticky =twokey =latchlock