Not something that should really be attempted. I tried unsuccessfully. Not sure it's meant to run this way.
I think rather than create a task within a task, which incidentally is not possible, you could create another task as normal from the main IPC and use preconditions in your Task processes to halt until other associated tasks reach their designated status. I've done this before where you say have "H/W" and "S/W" tasks and H/W one has to be completed before the other can continue etc.
You'll probably need to get "down and dirty" with BOO calculations etc for your precons, looping around the Task object. I tend to add a "Task Type" reference list to my tasks too such that I can more easily focus on the types of task I need to monitor. Depends on your design though as also by having different Task lifecycles kicked off depending on what you need to accomplish and later tetsing on lifecycle title would I guess also allow you to focus in.