Syclo:Mobile IM:Adding a field to BAPI export structure

I need to add bin location to the cycle count screen in SAP Mobile Inventory Management 4.2.1.  The BAPI is /SMERP/MM_DOPHYSINVDOC_GET and the export structure for the ET_ITEMS table is /SYCLO/MM_ISEG_STR.  Looks like I need to :

1. Add the LGPBE field (from MARD) to the /SYCLO/MM_ISEG_STR structure
2. Update the BAPI to read the value from MARD based on the ISEG (material document lines) field material and storage location.

There' s no append structure for the table and no apparent BADI / enhancement point for the BAPI.  Typically how is this done.

Thanks

Stewart