Trying a positive feedback loop with my mother often works to dial it back. For the last couple of years, I'd taken to offering to run errands for her before she thought to ask. For one thing, I'm always out and about anyway; for another, the way she asks annoys me, and my main goal was to head it off so I don't have to hear it. Well, unintended consequence: she's gotten more straightforward about asking (while still absolutely polite). She's also likelier to arrange things for herself. We're both happier!