You might begin by saying something like:
- If we're allowed to brainstorm...
- As long as we're in the brainstorming stages...
- If you don't mind me brainstorming for a moment...
One of those (or something similar) might work particularly well with anyone who’s had a more formal introduction to brainstorming techniques. Notice how brainstorming is supposed to encourage the addition of new ideas, without any emotional attachment to, or quick judgment of, these ideas:
- Focus on quantity: Quantity breeds quality .. the greater the number of ideas generated, the greater the chance of producing a radical and effective solution.
- Withhold criticism: In brainstorming, criticism of ideas generated should be put 'on hold'. Instead, focus on extending or adding to ideas, reserving criticism for later. By suspending judgment, participants will feel free to generate unusual ideas.
- Welcome unusual ideas: To get a good and long list of ideas, unusual ideas are welcomed. They can be generated by looking from new perspectives and suspending assumptions. These new ways of thinking may provide better solutions.
(taken from Wikipedia)
If your audience may not have had such training, you can always begin with an introduction to your introduction:
I don't know how many of you have ever used brainstorming in the workplace before, but, when I was taught to do it, they emphasized that it works best when everyone just throws out ideas as they come to mind, without worrying too much about judgment and criticism. After all the ideas are on the table, everyone can go back and select from the best ones. So, if we could brainstorm this for a few minutes...