Well your fishy essence, Since you do need to set the tone of your Reign on the Chair of St. Peter, you need to make the Papacy unique to your particular tastes and inclinations.
While i'm partial to burning due to my background, i generally prefer chemical burns, less trauma that way, and much more amusement for a longer period of time, progress you see.
Still, in keeping with the tone of your Papacy...how about a large pool of holy water filled with hungry pirrana fish, and a block and tackle to lower the heretic into the pool slowly. Leave his feet free so as to add to his despair (good for extracting confessions). Of course, tourniquets and "cut downs" are required to keep the subject from bleeding out prematurly when the femoral arteries are consumed. Should he confess and recant, simply release the tension and allow him to be completely immersed. It would at least show the infidels that you are serious and innovative
It also has the added benefit of providing the climate for blessing and exorcism.
Might i suggest CC Woody for the position of exorcist, seeing as how i seem to have this department under control?
Your indulgence please your fish n chips, but i must add that anyone knows how to inflict great amounts of pain. The process is far more effective when one adds a certain amount of mental anguish to the process. My favorite techniques have always involved the giving and removing of hope (along with certain body parts) from the heretic. At the end he must beg for death, and be in despair that his or her worst horror would be the possibility that they might live through the interrogation, with what physical "assets" they have remaining.