This time I had a planned c/s not an induction but I was like you and wanted to keep it a secret. We just kept telling people it was 'the beginning of May' or 'in a week or two' if they asked when, if they kept asking I just told them straight out that we wanted to keep it a surprise. Everyone was very understanding about it, I think they like getting that surprise text/message almost as much as we like sending it.