Although we obviously can't give Hashem anything and nothing can be added to Him, He formed a situation were we offer up to Him and serve Him. As mentioned by @ray, Rashi explains that the Nachas Ruach mentioned by the Korbanos is about the fact that He said and we listen.
Hashem did create a universe that we can add to. This is His system and adding to it is seen and accepted as if you were giving Hashem something.
Think of how when you feed an infant and he tries to put food in your mouth. This is a gesture that, although you don't need his (sticky) present, you accept and take pleasure in. Hashem doesn't personally change and is not personally affected by anyone. However, as with any emotion attributed to Him this can be understood as Hashem knowing, agreeing, and acting on the goodness of the deed.
In fact, by a human as well, an emotion is a recognition of a situation. The difference is that while a human is completely taken over and changed by the situation, Hashem is not changed. But the recognition and reaction is there. This is not a Mashal. It is inherently the same thing minus being affected by it.