Stock Flash and Relock WITHOUT USB

[Fua]

Great news!!!
I think I'm suffering from the infamous "my car charger ate my phone" syndrome. Or it sure looks like it. I have a Sprint Diamond running Mighty4 which recently stopped syncing. From reading around, it looks like a car charger problem (and the timeline matches, too).

So, I'd like to bring it back to the store for warranty repair; however, it's unlocked and flashed.
From the "How To:...", it looks like I may be able to flash stock ROM from internal storage.

Now, is there a way to relock the phone without USB connection?

Any help/suggestions will be GREATLY appreciated, as I may be SOL otherwise