Default proxy settings

I know how to change the system proxy settings for an individual user. 
But I need to learn how to set them for all users, even users who 
haven't yet logged in to a box and don't yet have a home directory. 
There must be a configuration file somewhere where KDE stores these 
values. Online searches haven't found anything useful, just detailed 
instructions for what I already know. Perhaps I haven't yet found a good 
set of search terms...
-- 
Dave Close