We had a lot of success having a QR code in a framed stand at our customer community booth during our user conference last year! Granted we were offering a $50 gift card, but still, people in the community were already very happy, but if you're doing an upcoming hosted event, it might be worth considering!
Obviously not a targeted cohort, but we had some luck there.
Maybe look at customers who've recently attended a lot of events if your company hosts several of them?
