Trying to make a bbcode feature

hello everyone, I'm currently trying to make a new bbcode(Keep in mind this may confuse some) The bbcode is to direct you VIA Xbox live to send a message. now I've got the code pretty much set but I am not sure how to make it grab the original posters name and put in the brackets {content} in this code

<a href='http://ift.tt/1tNUHC3}' class="bbc_url">Click Here for INVITE!!!</a>

Also afterwards I would like to make a button on my shoutbox that says Inv and you click it and it will activate the BBcode then they just hit shout and it works, I'm sorry that is confusing, I don't really know how to explain it at all.