Rather than searching for the perfect 4-segment run, I tend to look if a direct flight I have to take anyway can be reasonably replaced by two A3 flights with a change in ATH or SKG.

For example, when I need to fly FRA to LHR (ideally with some flexibility on the dates) I do not book the obvious LH or BA flight straight away. Instead I first try to see if routing on A3 metal would also get me from FRA to LHR with two segments on A3. Same for the return flight.

Most of the time the A3 flights take too much time, but every now and then I manage to collect 2 or 4 segments.

I also tend to decide based on finding A3 flights where I can use some of my upgrade vouchers.