actually my wife does his to me all the time if she isn't in a hurry to get up. She is just very conscious of when i'm about to come. She then stops/slows down/lightens her grip/goes in to a teasing mode, depending on how close I am. If i'm lucky, and she's into it, she will keep me really close for 10 minutes or so (seems like hours). By then I'm begging for relief. Take practice, and feedback. Let her know when your getting close, and she'll get the hang of it.