Hello, I'd like to say that using custom code especially sections and controls are not recommended as they pose problems for future upgrades.
Have you tried any OOTB alternatives? Following are a few OOTB alternatives you could try:
1. Use a button with an action "Perform Action". Specify a flow action and connect it to a sub-process shape that points to flow A (you can use when rules to route it to a specific shape within Flow A)
2. Run an activity on the button with the Flow-New method to re-direct processing to Flow A.
3. Use Tickets - these are not always recommended. Use judiciously.