Need to disable pointing stick permanently for all users before they login

Question

I need to disable a pointing stick on an old Dell D620. It's too sensitive and makes it hard to control the cursor. I have the command to disable it:

xinput --set-int-prop "DualPoint Stick" "Device Enabled" 8 0 

It works fine in a terminal window, but it doesn't stick. If I log out, or switch accounts, or even just let it hibernate, I have to rerun the command. Tedious, but tolerable. The catch is this laptop is shared by several users (separate accounts), some of whom don't have the dexterity to work around the problem until they can get to a terminal window. They can't even get to the login screen when it's acting up. So I need to figure out how to disable it once at start-up, for everyone, and persistently.

I tried several things for startup, none of which worked:

• Added the command to /etc/rc.local

• Created crontab with the line @reboot /etc/rc.local

• Copied rc.local to /etc/profile.d

To try to fix it on resume, I created this script:

#!/bin/sh

case "${1}" in
    resume|thaw)
        xinput --set-int-prop "DualPoint Stick" "Device Enabled" 8 0 ;;
esac

I put a copy in usr/lib/pm-utils/sleep.d. When that didn't work, I moved it to /etc/pm/sleep.d.

What do I need to do to disable this for all users, all the time, before they have to log on?

edit: ubuntu 14.04

edit2: edited the title to more accurately describe the problem. Also, I tried several of the ideas in the "how to run scripts on start-up?" post. They didn't work and I have no idea why. Even if they did work, they don't stick. Log out, switch account, suspend/resume, all re-enable the pointing stick. I need to switch it off somehow, and keep it off.