Storing Data in NVRAM during deep sleep

I’m looking documentation on storing data during server.sleep in nvram? I read Hugo’s post on Power Limitations below and I would like to follow the same principle in my application, taking readings once a minute then posting to the server every 15 minutes.

Hugo -

"Our nora reference design can run for around 3 years on 2xAA's when sampling temperature/humidity every 15 minutes. The next big impOS release adds wifi-less wakes, which would allow you to wake to sample once a minute but only transmit readings (say) once an hour, which could give you well over 5 years battery life despite a much faster sampling interval. In initial tests we've been able to wake, collect data & store it in nvram, then sleep in well under 100ms."