Vtiger Small Modification

I am looking for a small extension of vtiger functionality. In Vtiger we have the option to export a invoice to PDF. I am looking for a small extension, I need an option to export multiple invoices to pdf. To be more specific: The page in Vtiger which lists the invoices, in that page, i need a option called " export to pdf". Here once i select the multiple invoices & click this button, i should be able to export all the selected invoices to PDF, at one go. If you have any doubts let me know. Note: Need This on urgent basis.