Custom Breadcrumbs

[eluser]frankthetank[/eluser]
Well, basically iam building a forum similar to CI forums. I also need the same breadcrumb which is on the top of the page. Meaning, using different controllers that do make up a hierarchy.

For example:

1st index page => indexforum
2nd view a forum => viewforum
3rd view a thread => viewthread

These are three different controllers but from 1 to 3 make up a hierarchy. However, how do I turn this into breadcrumbs without statically saying ['index'] = www.site.nu, ['forum'] = www.site.nu/viewforum.