[development] Help coding "Firing module events after the page is loaded"

I have a vague recollection that hook_exit used to fire after the page was loaded, so that users would not be waiting for this processing to occur. (poormanscron relied on this, yes? ) I have a need to load some information for future use, but it takes a long time to load via web services calls. Anyone have an idea of how to get a page event to fire at the after the page has been returned to the browser? Feel free to just point me to some similar code if you know it exists.