If the Ubuntu boot loader is stored on the Hard Drive, is there an alternative to loading the boot loader from the hard drive?
Can it be stored on alternate storage such as a CD or even an external hard drive and used to boot the user's system?
Yes, you can.
You just need to choose where to install the bootloader in the installation process. Watch out for where is mounted your media (eg. /dev/sdc1) and mark it by choosing 'advanced' options just before you confirm, when the screen shows you the resume of the information, where the new system will be, and stuff. Something like those images in this link in portuguese.
Or, if you have a system running already, change the location and reinstall it. There's a lot of information about how to do this.
My sister have a laptop running windows, and sometimes I took it borrowed to do something. Asked her for install a linux partition on her disk and she not wanted because of the bootloader before windows starts, and was affraid of any problem with her own data. So I maked a tiny place in her disk, and install ubuntu. In the installation settings I done what I have explained: with a usb plugged, choose its location for bootloader install and done.
So I changed the boot options in pc setup, saying for computer try to boot first by usb, then the HDD.
When my usb is plugged, the bootloader works and starts ubuntu, when not plugged, windows starts and even know nothing about linux existence. (:
Hope it helps, sorry with any bad english.