How to add a mentions system to BBPress

Hello,
I am wondering how I can add a mentions system to BBPress. Is there a way to do it without using BuddyPress? I really do not want to install something that I will not use half the features out of.

Just so we all know what this is about, when I say mentions I mean something like @Alex. I guess another word for it would be user tagging.

Any suggestions?
Thanks.