Tom;

WD-40 will help lube immediately for picking attempts (but the key is a 5 or six pin, doublesided WASO blank and if any nonlocksmith owner can successfully pick it, they're a better man than I, Gungha Din!)...but WD-40 wont do anything to prevent sparks (and sucks IMHO as a longterm lube)...and if tank is truly full of stale fuel, then it has less octane than extra virgin olive oil...it'll burn sure, but need a lot more than you fumbling around with and at the fuelcap to ignite it!!!

My advice: Feed fuelpump by way rubber line running to a reserve can of fresh fuel in passenger footwell (or in front of radiator if your worried about it in passenger compartment, see below), drive vehicle to an experience locksmith and ask them to make a "key by impression"...and have them make a copy once good function is verified...lube lock with Tri-Flow!

Drain tank of stale fuel by loosening brass plug.

...and PLEASE stop with the gasoline exploding when you look at it crosseyed bit...Gasoline is great stuff, and an unsurpassed way of relatively safety storing and carrying around a huge amount of BTUs, BUT, it ONLY explodes if combined with air in a relatively precise ratio, then compressed and ignited...otherwise it just burns...sure, care is called for when working around it but just as much care as when using paint thinner to clean your brushes or filling your lawnmower, or spraying carb cleaner while servicing you SUs (No Smoking, please, around atomized hydrocarbons!), but nobody make a big deal of that...

Cheers