filtering the URL

when I set up categories in the CMSB as a drop down list... the client sets each item to it's corresponding category, and I set up the pages to call up the category like this:
www.samplesite.com/products/?category=italian
And this works great! But now the client has requested the ability to assign a product to more than one category, to which I just converted the drop down to checkboxes, however now I don't know how to call up the category in the URL since I know these multi-value checkboxes work a little differently... let me know