Dividing requisitions among buyers - can we Default Buyer by supplier or category

I am looking for a functionality that will help divide up the work among buyers.  Currently we assign default buyers by item, but we also process many requisitions which are not item-based.  These requisitions all go to the autocreate queue and several buyers have to review them before they know which reqs are meant for which individual buyers.

In the buyer setup, a buyer can be assigned a single category, but we have 40 categories and only 5 buyers.  It does not seem to allow multiple categories to be assigned to a single buyer.  This functinoality seems to be a restriction more than tool facilitating work division.