I'm with you on using attic heat for winter. You might get some good ideas from what I've been doing, described here:
http://ecorenovator.org/forum/solar-...bottom-up.html
It has the advantage of using a radiant barrier which keeps the attic (and house) cooler in summer. It also uses that same radiant barrier to collect and concentrate any hot air collected up there and brings it down to the house via a fan in winter. The control and construction regime for using a system like this has to be well thought out ahead of time. It's not something you do over a weekend or two.