What do you mean by that? Want for more what? Want for you? For sex?
The ideas are endless, but they all involve you removing yourself from the scene. I once gave my main plate a ride home, we made out in the car for 10 minutes in front of her house while I put on some cheesy 'romantic' music, and then kicked her out of the car. I sometimes, but not always, walk her to the metro station, make out and then push her off to catch a metro. If by wanting more you mean sex, make sure to shove your hands down her pants while you're dropping her off. I've more than once fingered her until she had soaking wet panties on the station platform, only to push her in the metro and then run off.
The trick is simple: Make sure you are in control of when you leave. However, don't leave unexpected, just announce it early on and then go, even(or esp.) if she begs you to stay.