You can use Hallucinations....
Center Location 1 on unit,that you want to kill ,and that he would left his corpse....
Trigger:
Player you want it to hapen
Condition:
Current Player suffers exactly 1 death of unit that will leave his corpse
Action:
Create 1 unit that will leave his corpse at location 1 for player 12 and aplly the properties(Hallucination)(invincible)
Wait (You can count how long Hallucination could hold on)
Preserve trigger
I dont know if its would work,but it worth a try....
And I think I`m crazy ,but you can try to disable doobat state on hallucination too

Or u can do it like that:
Center Location 1 on unit,that you want to kill ,and that he would left his corpse....
Trigger:
Player you want it to hapen
Condition:
Current Player suffers exactly 1 death of unit that will leave his corpse
Action:
Create 1 unit that will leave his corpse at location 1 for player 12 and aplly the properties(Hallucination)(invincible)
Condition:
Always
Action
Set Energy points for any unit at Location 1 owned by any player to 100%
Preserve trigger