Ask each participant to build on his colleague’s ideas, improving them or using them as inspiration to generate another three ideas.
If the idea of this is to eliminate fear in sharing, wont the lack of anonymity contribute to the introverts' fear of expressing their ideas? also if this ends in a group discussion, doesn't that mean that the discussion will likely be dominated by a select few? I'm just not sure that this is a reliable method to make sure everyone is included.