garden stores sell adapters that go on the end of hoses and suck up fertilizer. but honestly, i don;t think you're going to be able to control the amount of nute accurately enough. you're better off using a bucket for those times you add a nute
I always put the water in a bucket for a min of 24 hrs before watering to give the chlorine in the water time to evaporate. The chlorine can cause the plants problems and the healthy bacteira in your soil. But if you are having good luck with the hose why stop a with a good thing eh?