Here's the fix...
Here's the fix...
From an authoritative source, i.e., someone who found himself in a similar situation: Drill a hole on one side of the center flange/handle near the keyhole, then drive a nail--a wood screw might give you better "grab"--in the hole until it engages the lower part of the cap in the filler neck. [A locking fuel cap is composed of two parts--the exterior, locking handle and the interior, filler cap portion. Engaging the key locks the two together. This is also why simply drilling out the lock will not work, which was the first thing that popped into my head.] Allegedly this allows you to turn the cap as one piece without fear of damaging the filler neck.
Sounds reasonable, doesn't it? When it isn't so obscenely hot outside I'm going to give it a try.
UPDATE: Well, I finally got around to giving it a try. It worked like a charm, shockingly easy.