conditional field_collection field

Hi,

as far as I know until now it's possible to make conditional fields within a node or a field_collection, but what would it take to make the fields of a field_collection depending on a field of the collection parent node?

for better understanding:
Node xyz:
- Field A
- Field B
---Field C (like collection ;-))
---Field CA
---Field CB
...

Field CB depending on Field A ?!?!

Thanks for your time!

Greets
ifux