This is not a Perl problem, this is an HTTP problem.

There is no way, in HTTP to specify "Go back to the previous URL and open a new window for this other URL" (nor, for that matter, any way to open a new window in HTTP period).

You might generate an HTML document with some JavaScript that opens a popup and then goes back in the history - but that's a hidious solution.

You could also assume that if the user has their browser configured to open Excel documents in a browser window, that they can choose to open a new window (or tab) when they want, and are capable enough to use the back button if they want to go back to the previous URL.