VBA SAP GUI Scripting with SAP Logon as different user

I have a piece of Gui Scripting which opens a connection to a specific SAP system. This works fine as long as I open SAP Logon as the same user as the one that is logged into the machine. However, I now need to open SAP Logon as a different user. So far so good, everything works if I do it manually, but in the Gui Scripting line

Set SAPGUIApp = Get Object("SAPGUI")

SAPGUIApp is not set correctly (it remains empty). Does anyone know how to fix this? Do I need to specify in which user context SAP Logon is running? If so, how do I do this?

Know someone who can answer?