This video from Simon Sinek outlines a way of brainstorming which may help you. Starts about 2 minutes in:
- ask each member of the group to return with 15 new ideas within a timeframe
- elicit 2 or 3 from each person, but with “boggle” rules: if someone said yours already, cross it off your list
- enhance and cross-fertilise as you gather
- bucket and colour code (red – never, green – yes, now, yellow soon) depending on your outcomes
for other ideas for your offsite see here.