"Hey, me have good time, me really like spending time with you, but honest me not look for anything serious. Me no mean hurt feelings or lead on, but me would like to continue seeing. But me not want to lead you on, me not looking for anything serious, me just want to have fun and see what happen. Me hope you no take too hard, and me hope we can still hang out."
Then just keep it up until she realizes you're not interested, she'll probably try and change your opinion if she's really into you, but that just means a few more days/weeks of sex, and in the end you'll be clear because you laid it all out up front.