Why do you need per execution instances?
Do you want to activate the same ability multiple times simultaneously?
If so, perhaps you can do what you want with replicated events or target data, since I believe those are bound to the ability spec handle. It would be a bit more generic and limited, but you might be able to achieve what you want.
These would be the InvokeReplicatedEvent family of functions or CallServerSetReplicatedTargetData AbilityTargetDataSetDelegate