Since the coffee grounds are at ambient temperature, there is no way to prevent a temp drop when you first pour over.
Don’t worry though, it happens with every single brew method. The methods specify the water temp that you pour/brew with, not the outlet water temp.
Sounds like you’re doing enough to preheat your brewing eqpt, but keep in mind if you wet the filter then let it sit for even a minute, it will be cold. Make sure your v60 is nice and hot, that will retain temp much better than your filter.
Overall it sounds like you’re keeping an eye on some of the right things, just don’t worry so much about outlet temp so long as you’re preheating as much as possible. Cheers!