There is no easy way to achieve this. I didn't try it myself nor did I see it in a working solution but I remember a discussion in a German forum where somebody tried it with a portal. He was facing severe problems.
SeedCode made a "Hierarchy" template, which I bought last year, and use on a regular basis. Works great.
But I don't see it on their website ( http://www.seedcode.com/ ) anymore. Maybe if you ask them nice...
Hope that helps.
I have found two solutions for the problem. 1)simple WBS building on and disassambling for ex: 5 to 4.1 , 6 to 4.1.1 , etc. and back.
2)graph based algorithm to form unlimited branches with sets of descendants and ancestors.
Both are fm scripted by me. please contact if need (http://progressoft.ru/contacts.html)