Hi ,
use this user exit MEREQ001. in this use following exits.
EXIT_SAPLMEREQ_001 Import data from table to Purchase requisition screen.(check this parameter you will have all values IM_REQ_ITEM )
EXIT_SAPLMEREQ_003 Export data from Purchase requisition screen to Table.
EXIT_SAPMM06E_016 Import data from table to screen fields.
EXIT_SAPMM06E_018 Export data from screen to table
in this add EBAN table for you custom fileds by ci_ebandb.
Regards,
Gurunath Kumar D