Kinda hard to encode it in /etc/passwd, which separates entries with newlines and fields of an entry with colons.

Of course, you can activate some alternative user database in /etc/nsswitch.conf and then you can have your usernames with newlines in them, but at least half of the tools on your system that process usernames will take that personally…

ps outputs a newline after every entry. What are you trying to accomplish?

Do you have a username that contains a newline character? If so… why?!