Looking at the generated .vbs file it appears that it “only” executes the .egp (or a project within the .egp).
If opening the .egp with WinZip you find a file project.xml. All the connection info like the server to be used is stored in there. And this project.xml is written/modified when you save your EG project.
I therefore would conclude that you can't force the execution server with the schedule task (unless you write your own .vbs).