How to copy topic/thread with live post updates in both threads/posts

[fn9mm]

Hi,
I have several interesting posts in different subcategories.
I'd like to make one category/forum named 'Treasury Box' where i'd like to keep a copy of all interesting threads on my site.
The problem is that once I make a copy, I have to different threads from the moment i'd copy them (a reply in thread A will not appear in its copy, thread B), thus making it no LIVE copy.

The most logical way to do this in another way would be :
- moving interesting threads from different fora to 'treasury'
- moving them back to original locations and leaving a permanent redirect in 'treasury box'

That way people can only reply in the right thread.
This moving thing is quite a handfull tough.

Is there anyway to copy different threads to one forum (treasury) and keeping the 2 threads updated is a post/reply is made in one of them ?

Advice and hints welcome, tia