FWIW (reviving an old thread)-
Putting an OCA with bypass through the CGN with RFC1918 space will actually work just fine. We (Netflix) don't formally support it because of the vast number of non-standard CGN implementations out there, but if your clients are in RFC1918 space and the next hop router from the OCA knows how to reach them, it will just work. We only use BGP to inform our control plane, not for local routing. Any traffic not served via the OCA will go through CGN as usual and out peering/transit. Note that it does complicate troubleshooting for both sides.
And yes, IPv6 is fully supported by every piece of our infrastructure; the issue is TVs and STBs that do not support v6 - but we have finally seen the largest device manufacturers commit to supporting it (if they don't already on their late model sets) so that should change year over year.
-Dave