You can use this script from ruario https://gist.github.com/ruario/215c365facfe8d3c5071
It will install the flash player to /opt/google/chrome/PepperFlash/ on my Centos 7.3
Both Opera 42 and Vivaldi will detect the plugin.
However it breaks the plugin for google chrome - removed the folder from /home/ocky/.config/google-chrome/PepperFlash/ ... but if you don't use chrome you are OK. You will need to run the script from time to time to get the latest plugin.
