How do I display unsupported emoji on OS X Yosemite
I copied these two files from El Capitan and replaced the default ones (I recommend making backups):

/System/Library/Fonts/Apple Color Emoji.ttf
/System/Library/Input Methods/CharacterPalette.app/Contents/Resources/Category-Emoji.plist


After a reboot I have all emojis in Yosemite.