Attach call activity to a parent process instance by modification

I would need some help on an advanced requirement.
I was lately working on a “step back” functionality for our bpmn flows, and I managed to do it by using the process modification feature.

Whenever the bpmn engine hits to a usertask, I store the process id and activity id in redis cache to later bring them back if someone tries to step back.

However, we have a root process and use the “call activities” to run some external bpmn flows which were supposed to be reusable in many other flows.

At this point, my “step back” function fails because when a “call activity” starts and completes, it doesn’t live in the system anymore and its been removed. So the process id I stored for it becomes useless.

I can specifically create a new process instance for that “call activity” and use modification to start it from where I wanted.

What I’m looking for is to attach the newly created process instance to a parent process instance and do the modification on the parent to use this like a child.

I guess there is no way of it right now ? but may be I can create a feature request for next releases if it makes sense ?

Or any better ideas ?