During the early days of Reed Switchboard, one of our first events consisted solely of hauling a blackboard outside and taking photos of alumni with their passions written in chalk behind them. (We aggregated on Instagram and online here.)
In addition to being a fun way to get alumni to stop and talk, it was also a way to get them to think about what they might have to offer or want to ask for.
Reunions is perhaps the best time to introduce Switchboard to alumni—even if you can't get them all to come to an event. Occidental College included this ad in their reunions booklet: