Hi Archar,
I don't think you will be able to debug using External Breakpoints here. ( When your custom method is called you can use the old technique to introduce Endless loop and debug via SM50/SM66 )
Did you check the BCS trace file? It should be available under Statistic Node in SOADM/SCOT.
Or normally the BCS trace files are written under logical File name "WORKFLOW_LOG".
You can get the physical directory by calling FILE_GET_NAME and check.
R