?
Since this is a GOS screen you have the option to add your own service to the GOS options, see Creating New Object Service - Generic Object Services (BC-SRV-GBT) - SAP Library in it you can call the standard class but in the end send a mail.
You can look in table SGOSATTR and enhance the standard class as well.
No need for workflow in any case - simply send the mail (class cl_bcs).