An easy way to achieve it is to alter the preference file for a specific user.
Go to the user's home directory, and find the file: Library:Preferences:com.apple.finder.plist
Modify the file using property list editor or text editor: change the key AppleShowAllFiles to true.
Restart all finders: type killall Finder in the terminal.
Done. To revert to previous settings, change the key value back to false.