If you have a backpack sprayer, you can use a diluted soap mixture (3-4 Tbs liquid soap per gallon of water) and hose down the entire tree, concentrating on the underside of the leaves. That will help knock down the aphid population and let the ladybugs catch up to them quicker. You can also try just hosing the tree down with a sharp stream from a hose, to try to knock as many of the aphids off the leaves as you can. Be careful with that method, though, because you could knock the fruit off the tree if the stream is too strong.