I was also 4cm at 40 weeks. I had two s&s, got acupuncture, ate spicy foods, dtd, walked such long distances, bounced on a fit ball, had hot baths, used clary sage oil... Just to name a few things...
I ended up being induced by ARM and was 5cm on induction.
Anyway, it'll happen when it happens as you know no matter what you do/try... It's frustating having people asking all the time so turn off your phone, like OP said get your mum to take your little one out for the day and have a relaxing bath, stay in your pj's, watch chick flicks...whatever it is that makes you feel relaxed and pampered!
All the best