Say "Things have been crazy this month ( because I recently learned I am in a cult), you know how things are some times, maybe next month (if hell freezes over), how are things going for you?
If you play it right you should be able to get away with it. It's all in the attitude, if you think that these people have some kind of right to know anything about your life, then you might slip up and say too much. The fact is the elders only have the power you give them. You don't owe them any particular explanation, say just enough to get them off your back without arousing suspicion, really the less said the better, then change the subject or take your leave. If you don't act guilty they won't have any reason to think you don't have a legitimate reason to miss service.
As I am writing this I am thinking how strange it is that any adult would have to account to another person who is not their boss or spouse. It's your life! Crazy cult.