Yes, the API for handling CSRC values in outgoing packets is half missing
(some methods as the one you mention are declared but not implemented).
Most of the low level functionality for handling contributors is however
implemented, so it's a matter of coming up with a good API to set CSRCs
for the outgoing queue and implement it. This item has been for a long
time in
the TODO list but since it hasn't been requested so far, it has been sort of
forgot.
Would the currently declared methods (addContributor and removeContributor)
work for you? I'll probably look into this issue within a few days, so any
suggestion or contribution would be very welcomed.