Uma maneira simplista seria adicionar echo OFF > /sys/kernel/debug/vgaswitcheroo/switch
a /etc/rc.local
antes do exit 0
, para que fique assim:
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo OFF > /sys/kernel/debug/vgaswitcheroo/switch
exit 0