To the best of my knowledge, you can't. If you're looking to take things to that level, you need to understand that SharePoint is largely a black-box wf host. You might want to consider creating a Workflow Foundation workflow and launching it from an event handler. You get a lot more flexibility that way, but lose all of the default SP integration. It might also be a lot of work, depending on what you're looking to do.
Disclaimer: I've never tried this, it's been on the list of things to do for a while, but I see no reason why it wouldn't work.