如何扩展redcarpet以支持自动链接用户提及？

On my rails3 application I want to use redcarpet to handle user's posts and the user comment section. As such I'd like to extend redcarpet to support turning @username into a link to a user on my site. I know redcarpet is written in C but is there anyway easy way to extend it in ruby? How hard would it be to write it in C? Should I just do this outside of redcarpet?On my rails3 application I want to use redcarpe