From field experience as a Korean-American and thus someone closer in many situations to Ask, (or even TELL!) I have found a lot of success on just pretending to be endearingly forthright: making a big show of asking all the other people whether they want the last dumpling a couple of times, asking whether they're sure, etc. The fact that my uncle, my mother, and I are similar in this and that they will often take me up on this to split/outright take the dumpling, showing clearly that I am, indeed, serious about my ask, helps too.