Custom Uri Scheme For Htmlpurifier

Recently I ran into a situation where I had to let custom URI like this to

<a href="ASSIGNMENT::222::HREF" title="authored_link_title">authored_link_text</a> to pass via HTMLPurifier. However, HtmlPurifier is deep inside Yii and I do not want to change framework code. So, is there anyway I can add Custom URI scheme like this one mentioned in the site or is there any other way to get around this problem. Can anyone please give me any insight into this problem.