I want my body rendered into a semi-rigid hydrogen balloon. My body had to have the same appearance it had in life, but the insides can be hollowed out to the madman mortician's heart's content. The balloon-corpse, now dressed in a suit and ready for service, is then placed inside a specially designed casket, upon which my remains are filled with lighter-than-air gas.
The casket is designed to spring all the way open so the corpse can fly out into the air. Inside the church (hopefully some sort of high ceiling bullshit), I'm wheeled into place before the altar. And at some sort of prearranged moment, the casket goes BANG! and flies open.
My body comes floating out rapidly, propelled by the opening lid. As the casket opens, the lights go dark, and a fiery combination of flashing red yellow and orange light starts flashing accompanied by high intensity strobe lights. As this occurs, with my mortal coil physically ascending into the vaulted nave ceiling, the theme from the Phantom of the Opera starts blowing over the sound system, accompanied by an evil and maniacal laugh.
As the shock is replaced with horror, several carefully placed compressed air cannons start launching frogs, locusts, fake blood rain, and other biblical plague bullshit everywhere on people.
And as an added touch, there will be daemonic runes, marks, and satanic maledictions written in UV sensitive paint, so that some strobe lights with black lights reveal the evil inscriptions.
This would be ideal.