This is hard to explain, but essentially, whether it's the first merge, or the second after vertical loops with the usual intention of rolling into Immelmanns, if I see us going into the head-on aspect at the top of the loops (before one of us rolls the Immelmann) I stay in the loop to entice the bandit to go for the head-on shot. I then avoid it, which is usually quite easy using any kind of slight nose roll to change Plane of Motion on him.
If he tries to hold and track for the shot, I quickly move to lead turn by pushing the roll into a turn. This may only give me a small angle advantage if he's observant, (and if I've watched his movement closely), but it's a start. Obviously, timing and practice make this move effective, and it is.
My rule is, unless I'm outnumbered or in a big furball, and need a quick kill to even the odds, I never go for the HO, but I want him to.