Interesting case. BTW, Pace, when I did my B rating many years ago, I flew over to CQF in a Seneca I with an instructor for the weekend to do the training. Halfway over on the way back, a sneaky hand went down to the fuel cocks when I wasn't looking, and the right engine shut down a few seconds later.
As you suggest, Pace, mid-channel is not the most sensible time to play with the fuel, and certainly not when flying at only 2000'.
I've never flown a Lance - I assume the fuel system is very similar to the PA28 series? Down by the left knee, rotary cock with a guarded off position?
One or two other notes for ditching - drop it in AHEAD of a ship if you can, having made sure they can see you and won't run over you.
If going low-level such as 2000', either wear your lifejacket (preferable) or wait until you've ditched to put it on - don't try and put it on and handle a dead-stick aircraft at the same time. It matters less about the pax, of course, but make sure a front-seat passenger doesn't obstruct the controls while trying to struggle into his.
Even in summer, average survival time in the water, unless protected by an immersion suit, is likely to be less than an hour. In winter, assume less than 15 minutes. If there are several of you, daisy-chain yourselves together using the long end of the lifejacket cord (THAT'S why they tell you to leave one end long) - when putting them on, make sure it's always tied on the left. Huddle together as close and tight as you possibly can to share heat and minimise heat loss. Have any kids in the middle of the group. Don't try to swim or kick or wave at ships. It uses too much energy and energy lost = heat lost. To attract attention, don't shout - use the whistle on the lifejacket. Its sound will carry much better than a voice, and you might need to save your voice for later.
As you ditch, or open the door, or climb out, ensure you take a deep breath just before, and make a very conscious effort to hold your breath. If the windshield breaks, or you fall in the water unexpectedly, or get a sudden inrush of water for some other reason, the gasp reflex as water hits your chest is a very strong one and your next intake may be your last, the air being slightly contaminated by seawater. It's a very fast way to drown.
Finally, if you want a really, really fun time, go do a HUET course (Helicopter Underwater Evacuation Training). There are a few companies that conduct this - I did mine at a place in Middlesborough. I assume they're still operating. Look it up - I won't name them here in case it's seen as advertising, but if you can't find it, PM me. The pool can simulate anything up to sea state 6, complete with thunder and lightning, wind machines, etc.