It looked as if the remaining part is still there. A bolt extractor "should" do the trick.
Also, make sure you buy the OEM replacement - just like the one you broke. The hole in the shaft is made so you can still drain the oil if it breaks, but also to "easily extract the remainder". The bolt itself is made to shear if too much torque is applied to the bolt, and thus to save the thread of the oil pan, which it was mentioned earlier is a pain to remove on the i6.