Near as I can tell, a snowblower works by using an auger to scrape snow toward a central input, and then using a fast-rotating impeller to blow it out the top discharge. One could possibly turn the snowblower into a leaf/yard vacuum by attaching a collection device to the discharge. The two best methods would be either a flexible, porous bag, such as a lawnmower bag, or a long hose for directing the leaves to another location. A snowblower's basic design should make it blow the leaves/grass/trash powerfully enough to direct it through a hose.

A quick search on google yielded confusing results. If anyone thinks this is baked please let me know.