Adding script to run at startup without touching rc.local
Solution 1:
I've managed this with the following which works well.
Create /etc/cron.d/reboot with the contents below. Note - It's been a while, you should check syntax.
@reboot root run-parts /etc/cron.reboot
Create a folder /etc/cron.reboot
From there it's a matter of dropping files in to the cron.reboot folder.