Hi Elwynn,
I would avoid using the created_via attribute for this purpose as the system is populating the value itself.
There is another object, rptmeth (table Reporting_Method), which may be useful for your requirement. It is referenced in the chg object and the iss object using attribute reporting_method. The developers never bothered to add it to the cr object but you could as a customized attribute (e.g. z_reporting_method SREL to rptmeth).
Rows in the Reporting_Method table can be maintained in the Administration tab, Service Desk --> Application Data --> Codes --> Reporting Methods