I would not recommend drilling a disposal either. Most disposals have inlets to connect a dishwasher drain. Your dishwasher drains into the disposal then drains out into the house drain lines. See http://homerepair.about.com/od/plumbingrepair/ss/anat_disposal.htm
If you have that inlet on your disposal and it is not being used by a diswasher, this would be the cleanest way to hook up your drain without going through the hassle of adding an extra connection in your main drain line.
If you have that inlet on your disposal and it is not being used by a diswasher, this would be the cleanest way to hook up your drain without going through the hassle of adding an extra connection in your main drain line.