Using getblocktemplate, you could just update the template occasionally, and generate as much work as you need on the offline system. Obviously you'll still need to update it timely for each longpoll. Then you need a return path for shares; you might be able to find a pool that lets you set your share difficulty high enough that you only need to do this about once a minute on average (though your variance will increase too) - unfortunately, my own pool can't provide that ... yet.
something like this would have been incredibly helpful for me a week ago when timewarner decided to be a tool and stop working 4-7 hours a day a few minutes at a time....
but ah well.
