Can't you find a moniter with vga lead and use that? Other then that even if he did get that usb thing I think with his laptop harddrive it needs power to power it up.. putting it in sata is easy but then you need power for the harddrive and your laptop would be already using one so this can be abit tricky.. maybe you can try the usb adapter , hoping it comes with the power funtion.. or plug it into a pc.. that's what I had to do..
Use the video out port and borrow an external monitor to see what is going on. You can then rescue whatever you want off the mashed machine over a network, USB or optical disk. You may need to toggle the output to an external screen by use of function keys or key combinations. For the laptop in question I think it's ctrl + F7 Or You don't need a third drive, you can keep an install of OS X on a second drive and use it as a Time Machine backup for the first drive, then boot from the second and restore from Time Machine on it. I've done this just to see if it was possible.