Hmm it might be possible in some way. If it isnt, you can set the heroes XP Gain rate to 0, and the create a costum XP system like:
Event:
Unit Dies
Condition:
Unit type(dyingUnit) == bla bla
Action:
Add x amout of xp to KillingUnit
Tell me if you want/need help with a system like that. But its really simpel to make, so I think you can do it yourself.