Can i execute bex workbook as background job ?
Yes, it is called 'precalculation'.
You will have to install a precalculation server for this ( an extra piece of software which can be downloaded from the SWDC).
If you search SCN & OSS for 'precalculation server' you will get tons of info.
Make sure you install the latest FEP patches, check your office version etc because this is quite important.