I honestly think this was such a fast moving crime that it didn't involve any time spent on lures. I don't think he needed that to get them moving.
I saw a post earlier about there being two perps because of the girls not trying to flee (because there was a second person behind them and they were effectively blocked from getting away). I can see that there may have been two people. But I would think that if someone was going to convince two kids to go along with them using a ruse that an injured friend or dog or whatever needed help down the hill, the person on the bridge would have been a woman, not a menacing male. The latter would have been farther on to ensure control of the victims.
I try to stay with what was simplest for the killer. It makes sense to me that a skilled predator with the boldness to do this in broad daylight would also have no issue with moving fast toward them and revealing a weapon and immediately giving directions before they could do much of anything. If I saw someone coming toward me at a quick pace and I was clearly in trouble, certainly if I was a child, I would be afraid to try and go past them toward the other direction, and afraid to turn and run for fear of being assaulted from behind. And on a precarious bridge, that would be even scarier.
My sense is, even if there were two people, this was a very fluid ambush-like situation and BG knew what he was going to do once he was in their space and he did so with not much effort. I say that also because of what appears to be a very short crime timeline.