You just have to be cool enough so that people start thinking "how can we organize the event so that X will also show up". Problem solved :-)
Another question: do you really want to meet people who would exclude you from an event just because you don't have a Facebook account? Friends don't exclude friends...
You seem to assume it's on purpose. When almost everyone in your circle has a Facebook account, it's easy to forget that person X or Y doesn't (usually depending on how close a friend they are with them).
Personally, I don't miss my account, but I can understand why others can.
Another question: do you really want to meet people who would exclude you from an event just because you don't have a Facebook account? Friends don't exclude friends...