I need a few days off, back in August!
In the meantime, have a look at the great conference Lean Kanban Central Europe which takes place in Vienna, October 22-23
When facilitating system design workshops in the past, what I did was the following: I stood in front of the first draft of the board that was just designed, said a few words about WiP limits and then asked the group „What WiP Limit should we put on this column?“ This was not a very collaborative process and it often led to long and tyring discussions if the limit should be 6 or 7 etc. Then I used a different approach: I divided the group into 2 or 3 smaller groups and told them to come up with what they think are the best limits to start with. After a timebox they reported back to the whole group. After this we formed new groups and discussed what we had so far. After this we consolidated the different drafts into the final one.