Hello Madhu,
via coding (except by a modification) it is not possible to influence the behavior of standard function modules.
But you can reach your goal by the so called SAP HANA Application Accelerator AddOn for ERP (aka SWT2DB). This an AddOn which allows to redirect SELECT and OPEN CURSOR statements to the secondary database via configuration. The redirection can be done per main program. So for your case for the main program of the function. But consider that the redirection is done for all SELECT/OPEN CURSOR statements in the main program and not just for a specific function.
Note 1694697 contains a guide for the tool (it is attached to the note). Consider also note 1696402 regarding the prerequisites.
Best Regards,
Florian