Success! I did a little more research and found a way to skip the GRUB menu completely. I found it here:
http://ubuntuforums.org/showthread.php?t=1302684
It's kind of a work-around because it didn't actually solve the issue of GRUB not working unless there's a keyboard, it just skips GRUB completely. However, it maintains the ability to plug in a keyboard and hold shift in order to get the menu and boot into something different.
Here's what the post says:
If the "GRUB_TIMEOUT=0" does not work, [...] open
/etc/grub.d/00_header and go to approximately line 238:
Code:
gksu gedit +238 /etc/grub.d/00_header
Find this section and make the changes in dark red, then save the file and run "
sudo update-grub".
Quote:
make_timeout ()
{
cat << EOF
if [ "\${recordfail}" = 1 ]; then
set timeout=-1
else
# Manually change timeout to 0
# set timeout=${2}
set timeout=0
# End manual change
fi
EOF
}
This should eliminate the menu display. It also preserves the ability to display the menu by holding down the SHIFT key during boot.
I'll mark this thread as 'solved' in a day or so, to see if anyone has any other ideas to actually fix my GRUB problem as opposed to skip it!