Mapping from CRM to R3

Hello.

First of all, when we create a quotation in CRM, it is replicated to SAP ERP.

Now, I have added 2 fields in CRM, in the quotation screen, via EEWB. And I want to map these 2 additionnal fields to 2 new fields that are in VBAK in SAP ERP.

I guess I need to read these fields in the BDOC, in the badi BADI CRM_DATAEXCHG_BADI, and then pass the data to the BAPI that will be called to create the quotation on R3.

My question is how can I pass those 2 fields to the BAPI?

I've read that I can use a BAPI Table Extension but I don't know how to use it since it doesn't seem to exist for VBAK.

Thanks for your help