I will get you started at least. I tried this in preview mode and it works, so it should work with on-demand There are two QV functions that might help you achieve this.
=osuser() will show you the name of the person logged into the operating system
=qvuser() will show you the user id of the individual if you are using section access.
As a general rule, if you can select a value in QV, you can display it in a NPrinting report.
So, if I was trying to do this, I would l would create a variable called vUser
In your NPrinting template, add a variable with vUser. Add to your Excel template.
I did a quick test and my variable displays my osuser() name in my Excel Report in the cell I place the variable.
Hope that helps move you forward