BP Custom Field replication - CRM to ECC

Hello Developers,

I have added custom fields to the CRM BUT000 (Business Partner) table, using AET.  Now,  I need to replicate these custom fiields to ECC.  We have configured, and are successfully replicating the standard BP fields from CRM to ECC.  However, the new AET custom fields are not replicating. 

Can you please help me by identifying BADIs, Enhancements, or User Exits where I can insert the required code in order to accomplish this custom field replication, on both the CRM and ECC sides of this replication?  Is there a document that describes what is required? 

We are running ECC 6.0, and CRM 7.0. 

Thanks for your help!

Duane