It's best to do it with a necro, using multiple recastings of the horde minion familiar to clear off the normal pumpkins.
The pumpkins spawn at a (very slow) set rate when the small ones are left alone (based on the decay rate - one decays, and new pumpkin respawns that MIGHT be a killer), but if they are deleted (dispelled in a horde minion, made into raw pumpkin pies, fed by the bagful to a goat, etc.) the replacements spawn much more quickly, including the killers.