Set scim as the input method for X under the locale en_US.utf8:
im-switch -z en_US -s scim
This will create a .xinput.d directory under your home directory along with a file that lists all of the exported environment variables necessary for scim upon startup. This file will be read by the 80im-switch script located in /etc/X11/Xsession.d when X starts up.
