Ah, a disposible camera type. If you replace the diode with a wire link, that will allow AC to pass (duh) and you can put a voltage doubler/tripler/quadrupler and a capacitor with a voltage rating of a least 1 Kv (in the case of the doubler). It will increase the power and reduce the charging time (assuming you left the photo-flash cap in).
Be aware that photo flash caps won't kill, but they can cause you or your unfortunate victim to do something that can result in injury.
Regards
Lachlan