Possible ways to achieve root?

So I actually don't have the S5, or any Samsung device for that matter, but a friend of mine does, and really wants to root their phone. I had no idea the AT&T S5 was so secure, but it's pretty interesting too. I've been researching for over 15 hours. I may not have been able to root his phone, but I think I have learned a couple things and maybe some possible root methods.

1.) Since using ODIN to downgrade would soft brick the phone, would it be possible to download the stock Lollipop update onto a computer, give the update super user access, replace the recovery with a custom one, or unlock the bootloader from the computer, then flash it through ODIN?

2.) Intercept any sort of OTA update, then alter it to flash a custom recovery or unlock bootloader? I don't know how you would go around this though.

3.) If someone hasn't taken the OTA update that patched the Stagefright exploit, could someone purposely use the exploit to allow installation of a custom recovery or even to unlock the bootloader since the Stagefright bug has super user access (or so I've heard).

Also, I'm sorry if these are stupid ideas. I know close to nothing about Samsung so everything I'm basing this off of is what I've read in the past 15 hours.