Hello Neelima,
In my opinion, such a requirement is not possible when the Header and Detail fields are too large in number.
However, if I consider your requirement, every set of Header and Detail fields might generate a separate purchase order (or may be anything similar to that). So why don't you use an IDoc receiver channel instead of proxy receiver?
If you use IDoc receiver, then accordingly there will be a multiple number of separate IDocs formed each with a Header and Detail field.
Hope my comments are useful 
Regards,
Souvik