Now, before everyone starts in on its a strength save not an attack roll, or as it has a range of 15 feet is not a melee attack:
Yes I've taken those rules into account when asking this.

So under the rules as written this is a strict no from what I can see, and I can live with that, but here is a hypothetical situation:

A creature is fleeing past you at 15 feet, you want to use lightning lure to drag it back and subdue it, it does not take damage till 5 feet away and all other criteria are met, but the lightning lure damage causes the creature to drop below 0 HP.

The question is could the caster drop the cantrip before the lightning damage actually killed the creature?

Unfortunately, no

While it's a clever idea, there is no way to mitigate damage from lightning lure. There is either damage delivered or no damage delivered.

Damage or no damage, there is no in between

Lightning lure does give you some control in how far you pull it, but it's either going to end up within 5' (and take the damage), or it will not end up in 5' of you and still be up and able to act on it's turn.

Some attacks can reduce a creature to unconscious rather than death

There is a rule for knocking a creature out, but that doesn't apply here because it's only for melee attacks and this is a strength save not a melee attack.

Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious and is stable.

NPC Death Saves?

Another consideration is whether or not your DM has NPCs make death saves. If they do, then this gives some time to stabilize the monster, but it also means you need to make sure NPCs actually die whenever you fight them.

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

If they do decide to go the NPC death save route, they will need to make sure to communicate when they are or aren't doing prior so you aren't left 'surprised' when an NPC gets back up.

As an anecdote, we once had our DM not 'kill' a downed NPC. It had never happened before and it never happened again. And it was a really frustrating experience to learn that we hadn't killed him. If a DM is going to have some NPCs do death saves, that needs to be communicated to the players.

RAW, it's possible --- but requires GM buy-in

As you point out yourself, the attacker cannot choose to knock out a creature with it because knocking out a creature required the damage to be made as a melee attack. (see Knocking a Creature Out in Basic Rules at DnDBeyond)

The spell's wording says it can pull the target "up to 10 feet", which suggests to me that one could drop the spell before pulling the target to the range where they get shocked, but that doesn't work like a magical taser.

Your GM can of course give you the option to use the spell to deal non-lethal damage. Since you asked for RAW guidance, I will point out this is not just a matter GM fiat changing the rules: monsters and NPCs dying immediately at zero hit points instead of falling unconscious is not a general rule, just an option the GM can invoke at their leisure. Most GMs will invoke it out of habit unless you remind them. If they choose not to invoke it, the monster or NPC is knocked out like a PC and will have to make death saving throws until stabilized or dead, unless it receives enough damage for an instant kill. (see Monsters and Death in Basic Rules at DnDBeyond)

The bottom line is that a GM can allow their players to knock creatures out with this spell while still adhering to strict RAW, but they can also choose not to, with the major caveat otherwise being that the creature will still require stabilization.