Unfortunately for you, it seems like Fastboot is the only thing that will save your phone, so it's time to roll up your sleeves and dig into the command line. You can lead a horse to water but you can't make it drink. You can give a person Fastboot commands but you can't make them type them in.
First, read up on Fastboot and what it actually does:
Fastboot - Android Wiki
artus88 has the solution and his commands are solid according to the Fastboot manpages but they're for the OSX version of Fastboot. You'll need to change them a bit based on what OS you're using. Is it Windows, Linux, or OSX? You'll also need the Flashboot binaries installed on your computer.
Here's a guide that seems more straightforward: