Arun,
I know you have already mentioned that ABAP Dataflows are not an option for you but scenarios like you mentioned are exactly where ABAP DFs need to be used. Not only is your development time significantly lower (Because it is a straightforward where clause pushed down to ECC) but also you will achieve performance which you cannot match with regular dataflows.
I haven't used the 'RFC_READ_TABLE' function myself but below is a link to the SAP supplement. Page 95 describes how to invoke a RFC function in general.
http://help.sap.com/businessobject/product_guides/sbods42/en/ds_42_sap_en.pdf
Good luck,
Chaitanya