I think the key is just keeping the contact and letting your light so shine, so that they can see all the good that comes out of involvement in an AC.
One of my former roommates was in medical school and residency and there just wasn't time or room for AC participation for many years. But in the last year, she has come to the tail end of residency and I have gotten her to come to a few social events for the AC in our area. She loved it and actually keeps up through our evites, letting us know when she can and can't come. To me, that at least shows she's thinking about it.