We wondered if this was a common problem and, through the magic of Facebook, we had AutoblogGreen reader Phil Tipper try it out on his 2013 SL Leaf. He said he used an insulated handle flat screwdriver and was not able to defeat the lock. "I admit that I didn't want to force the mechanism for fear of breaking it, it didn't look like that kid used much force at all," he said. "Maybe this guy's mechanism was damaged in the theft and now it's very easy to trip the lock out of the way." Fifty percent of a sample size of two isn't a reliable metric, but if you're worried about locking your cable in place, you can see some of Viau's anti-theft solutions here (in French, with pictures).
"The charge lock feature on Nissan Leaf is not intended to prevent theft of the charging cordset." – Brian Brockman
Turns out, though, that the white plastic bit that prevents the cable handle from working during a charge isn't really an anti-theft device. Brian Brockman, senior manager of corporate communications for Nissan North America, told AutoblogGreen that, "The charge lock feature on Nissan Leaf is not intended to prevent theft of the charging cordset. It is designed to discourage someone from unplugging the vehicle while a charging session is in progress. The trickle charge cable features a small hole in the release button to allow the owner to insert a lock to reduce the chance of theft." So, now you know.