Hi Nandu,
Recently I attended a refresher session on new features and functionality and based on the information I gained can I request your to ignore my earlier comments as those now appear to be an out dated design.
Achieving your goal looks much easier with new features and a recommended flow would be as follows:
1. PR created in ECC using Ariba Catalog option at line level
2. DPAS rating obtained as usaul on the PR in ECC
3. The DPAS rated PR's in ECC are imported in Ariba using standard Req Import functionality
4. The order is generated and sent to AN via Ariba P2O and is carbon copied to ECC
Please let me know if you have already tackled this in similar way or otherwise.
Regards
Vilas