There isn't a way within the framework to execute a flow within just the ItemProcessor piece of a step. For what you are describing, you essentially have two options:
- Write your own ItemProcessor to handle the logic yourself. That will also require you to handle the state management within your custom ItemProcessor.
- Execute the flow as a job step. You can execute a job from a step.
What is the logic you are attempting to run within the scope of an ItemProcessor? It sounds like you may be attempting to do more than you should in that single step.