Tell your client that manually created static templates is the only option.
For many to many relationship you have to store somewhere a table of relations like:
CC1 ACC1
CC1 ACC2
CC1 ACC3
CC2 ACC1
CC2 ACC3
CC3 ACC1
CC3 ACC4
...
No support for this in the current version of BPC.
You can try to develop complex VBA solution, but it's not a good option...
Vadim