No it is not possible and I highly doubt anyone will have made a mod in the 3 years since the last post of this thread. Just give the user admin access to forums.
If it was that easy i'd have done that long ago.
On my board there is a huge sub-forum which hosts an RPG. In this RPG many users are officers, which means that they are moderators of a particular sub-sub-sub forum of the GDR forum. I need to give someone the ability to add and remove users from the officer status, which means giving or removing their moderator privileges. Trouble is that I don't want the person with GDR admin status to be able to admin the whole forum, since there are "private" sections outside the GDR area which I don't even want him to see.