WordPress Category Hierarchy

Answer 1

I think you are looking for this.

http://wordpress.org/extend/plugins/scategory-permalink/

Answer 2

I think the best way to do what you want it's to transform your post to page.

Take your page:

1. Portfolio
   
   • Web
   • Animation
   • Print

Answer 3

Hikari Category Permalink is a fork of sCategory Permalink.

Red permalink links appear on mouse-over in the categories box which let you define the category to be used in the URL.

The example would result in something like: my_site.com/category/ciencia/my_post