There are two strategies that can be followed:
- The traditional one is to write a Custom consolidation algorithm, because a business with such dynamic requirements will often have a bunch of other things they want to customize. At that point, you don't really need to use POWN/PCON, you can just store numbers in some intersection and have the rule fish them out when necessary.
- A more "hacker" approach, which looks harder but is actually much simpler to address this specific requirement alone, is to have an Event Handler extender, triggered by the posted form, that picks up the data entered (again, the intersection doesn't really matter) and saves it in metadata properties. With that, you would be able continue to use the Standard consolidation algorithm, rather than writing a Custom one (which can be a daunting proposition).