Multiple S-users required for OSS integration to SAP

Dear all

My client handles the IT support for 4 companies. Each of these companies have their own SAP systems & therefore each company have their own S-number.

Currently, I can assign one S-number in the global settings & then I can assign one S-number per user.

The problem however is that each user can post an OSS message for any of the 4 companies & therefore need to be able to specify which S-user should be used at the time of sending the message to SAP.

Any ideas???