Jam an old Philips head screwdriver into the opposite side of the rivet that you're trying to drill.

Use a sharp 3/16" bit and a drop of oil to help lubricate / cool the bit. Bosch makes titanium bits that work really well against the hard stainless steel of the rivets.

Use the screwdriver as a handle to keep the rivet from spinning. Takes more than two hands unless you've got a way to hold the casting in place.

Once you get through the "collar" of the rivet, stop drilling. Use the Philips head screwdriver to drive the rivet through from the side you were drilling on.