Recruit mercenary pezhetairoi, for goodness. They can take a lot of heat off your lines during the battle if you put them in the centre. By the time any of them get through your pikes in any noticeable numbers the wings will already have been routed and you can crush them. If you set them to look for enemies to kill instead of waiting for them to attack you, even better, because then the enemy will just charge, get impaled, then stand in front of your spear hedge, wondering what to do, making the occasional foray into oncoming spearheads, and being generally tied up until it's time to get flanked or reared. Or your own Iphikratous and Epilektoi would already be good enough. Really. And get some Xystophoroi! Hippeis are pathetic. Xystophoroi are armour-piercing. Just the thing to use against their triarii. And if you're not averse to it, get some sphendonetai. Those are wicked cool against hastati and principes.