Begin by explaining that although this process is open to anything coming forward from participants, nevertheless, if you want your proposal or ideas to be sconsidered within the strategic plan, they should fit within one of the five areas. Point to the news wall where you have set up fives labelled sections (New Markets, Financing Options, Human Resources, Product Development, Collaborations). Topics that are included under one of these areas will find their way into the plan. Things that lay outside of these areas are just as valuable but we can't guarantee that we will have the time or space to deal with them.
Then you let the meeting go and invite people to post their proceedings in one of the five clusters.