ok, got it. Your thought was correct. I have to use "Run as this user" and select the TiWorker/TrustedInstaller.exe. Here I get what I need for the cmd.exe: "NT SERVICE\TrustedInstaller, Owner (Default Enabled)" .
So, can you please add trustedinstaller as item to the RunAs dialog which does this:
1- look if Trustedinstaller is running and if not start the trusted installer service
2- call Run As this user and use the TiWorker/TrustedInstaller.exe
3- if TrustedInstaller was not running stop it again otherwise leave it running