You can simply change it a bit to not involve a graveyard, even a simple one. Just make it so that "a creature killed gets its data 'stored' in the Well". That Well will replicate that creature when its ability is next used. Of course, this changes it slightly from 'last' card killed to 'first' card killed since the last use, unless there's a code to overwrite the creature inside of the well, but it then technically shifts the generation onto the card itself, instead of some abstract 'graveyard' that Zanz wants to avoid.
The only significant issue with this is that the Well has to be on the field at the time of death or this to work, which is a potential balance factor if anything.
