Add the ability to specify the settings folder so that Processing can be portable

Hi, I'm working in schools and I would to use a portable version, usable on USB stick. Also because there are securities, and as I work in different school there are different securities. On Processing3 I didn't find all the option I could find in Processing2 preferences to make quite portable (because it still write in c:\Users\AppDatat\etc

Thanks a lot for helping me.
