Hi Sangameshwar,
I think your client has already implemented the functionality in this way. It's not an easy task to save the order in CRM when it's already set to get saved in R/3. If your delivery and other processing of orders are done in ECC, then usually client goes in this way.
The way to get order saved in CRM is, to create transactions and replicate the same to ECC via middleware. But this is not a quick doable thing.
Thanks,
Faisal