When my multi-wire cutter broke, I either used a chef's knife or my normal cheese cutter, an Amco: http://www.getprice.com.au/images/uploadimg/1043/350__1_4671-.jpg
Once I learned a trick, I now use my Amco all the time. The trick was, when slicing a round ball of mozz, first cut the ball in half with a knife, then use the Amco on the flat face of the hemisphere; worked much
easier that way. Another benefit to the Amco is three different cutting widths; my multi-wire cut the cheese thicker than I wanted (I would just rotate the sliced ball 90 degrees, slice again, and spread the matchsticks on the pie).
I wouldn't recommend using the Amco if you normally cook "pies for a crowd", but cooking one pie for myself, it works great.