This app was mentioned in 3 comments, with an average of 1.00 upvote
Low-burden app that is PoGo specific (Caffeine is not) is Awake! https://play.google.com/store/apps/details?id=com.rarefill.awake
So although you don't want another app, I still recommend it as the appropriate tool for the job you want to be done.
Whenever I know I want to walk around and hatch eggs for instance but inconvenient to spin stops or catch things, I just launch with Awake! instead of the usual way. and keep the phone upside down in my pocket for a while.
https://play.google.com/store/apps/details?id=com.rarefill.awake try that one :)