How can I install Adobe Flash manually or without giving root access?
Download the dmg from Adobe's website. Mount it and right click on the Install Adobe Flash Player.app and select "Show Package Contents."

Drill down into Contents > Resources:


Launch the Adobe Flash Player.pkg:



When the plugin installer launches, go to File > Show Files (or CMD + I).


There you will see a list of the files it installs and where. You'll need to use something like Pacifist to extract the contents, but once you do, you can install the files manually. And yes, the install would be just as clean if you used the pkg to install the plugin. It's not any safer, it's just an alternate route that doesn't have the Adobe wrapper (so it doesn't use Adobe's proprietary installer).