using BAPI in extractors for feeding data to BW

Hi,

I have a requirement where ,I need to load the Data.

Presently They use BAPI_ALM_ORDERHEAD_GET_LIST to download the data into XL sheet.

Now New requirement is to insert this BAPI into function Module that will act as extractor that will feed BW using SBIW (Extraction By function Module).

Client will not use all the fields that comes from the BAPI , They will select few of them

the extractor can be a total Abap (using the BAPI) or can be also starting by Extraction from DB View then enhanced by the BAPI .

Can U please let me know the easy way for it.

Thanks in Advance.