BDC for custom HR Infotype

Hi folks,

I've gotta unique requirement. I need to write a BDC for a custom defined HR infotype, that needs to populate the fields in the screen based on the values from some other fields in the same screen. I make it clear here that the data of other fields are not in the database tables. I need to read the fields of the screen dynamically which i can do using some FM.

But since this is a BDC with CALL TRANSACTION, I cannot read a screen field that is available only in the future (after call transaction) coz the values of the itab needs to be populated well before that. Has anyone gotta solution??

Cheers,

Sam.