Hi
In my experiece with IHC & BCM, Bank communciation management approval was done only when F111 is executed to send the file to external banks but not between IHC and subsidiaries.
Due to the fact that you need to use program RFFOEDI1 - IDOC message from F110 in subsidiary to IHC, which then will generate payment Order, I would reckon that you cannot route F110 to BCM in subsidiaries and that BCM need to be with Payment medium workbench, for this reason we used the segregation between proposals and payment runs in F110 as a way of approval process.
So the process flow should be as follows: F110 in sub -> IHC in Head office -> F111 in Head office -> BCM in Head office -> out the door to external bank.
hope that this helps
cheers