
If you don't have Tactics, take 2 centaurs and elves. Arrangement: elves + a strong, expendable unit + 1 centaur + 1 centaur (the main thing is that the expendable unit is more attractive to the dragons than the elf stack; an even number of units is needed for a successful block). The Azure Dragons eliminate the expendable unit. Then, proceed as before.
You can also take, for example, 5 centaurs (2+1+1+1) and a ballista. There are many options.