OK, so the documentation is correct in that you cannot take an AP directly out of the box and convert it to survey mode. I just tried that and it I cannot get to the local status page at all.
https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Conducting_Site_Surveys_with_MR_A...
I can see a way around this possibly as Meraki will give you a 30 day grace period for licensing... So if you add a new AP to a network, ensure it's all connected to the dashboard and all, you'll then have 30 days to convert it to survey mode before it goes offline. Once it's in survey mode it should continue to operate as long as you leave it in survey mode.
But, that's just a guess.