I don't know if there's a specific portion that is usually used (others might know, though). I think in this case I'd say "you hold the syringe" and (assuming there isn't a more experienced voice to make a specific recommendation in the next few minutes), shoot what you are comfortable with.
That said: eventually it will be a really good thing to get these kinds of numbers to shoot! We keep saying it, but it's true-- Lantus is very good at giving flat cycles at low numbers, so when you get a pre-shot like this, it gives a chance at a cycle of safe, pancreas-healing numbers. I understand, though, that a night that has severe thunderstorms on the horizon (stressful for all involved-- does Sprocket get scared and hide in thunderstorms?) may not be a night you want to do it.
The only other thing I'd suggest is that, if you haven't shot yet, get another test in. He may be on his way up anyway (like he was on the evening of 5/11), which might make it less stressful to shoot.