How to submitt the real username into created_by_field in DB when sending an Inbound WebService to S

There are different users sending an Inbound Webservice to Siebel from an external application:

The customer would like to achieve this:

the real user from external application like "Horst Schmitt"  should be authenticated by Siebel and as result at the database the system field created_by field should be = Horst Schmiitt and not SADMIN

Is it possible to achieve such a requirment ? if yes, what is the best approach ?

thanks