It 'a good idea to make the conference also open to outsiders. In addition to meetings in the parks, as you suggested, I think you could also open the attendace of some events to general public. Doing in this way, you could allow people to freely attend the conference, primarily calling for university students. For example, you could also make arrangements with Universities to provide ECTS for the students who participated.
Where you there?
Marty, did you end up making it to the conference? I was so busy that i could not even say hello to everyone…