I think you should stick with a specific emoji grouping, such as the forum ones or the iPhone ones, since you really wanna do this.
Allow players to use certain 'keyboard' emojis. Something like having a command where we can pick which 'set' we want to use.
Such as the iPhone emojis or the Forum emojis, etc.
iPhone Emojis:
http://emojipedia.org/apple-emoji-list/