how to write a page to the cache from a cache sweeper

I've got an expensive page which I want to store in the page cache. The conditions under which it needs to be updated are such that it requires use of a sweeper object, no challenge there. The wrinkle is this: instead of simply expiring the page in the sweeper and lazily waiting until the next user requests the page to generate it, I'd like to go ahead and regenerate the page in the sweeper. Any tips on how I'd go about doing that?

- donald