Possible to automate Excel running on desktop from web app?

We are upgrading a VB6 desktop app and I am investigating the possibility of converting it to a web app. However one of the main features of this app is that it automates Excel from the VB6 code; see Automation

Therefore, is it possible for a web app, either from server-side code (running on web server) and/or client-side code (running in web browser), to control an Excel executable running on the client's desktop?

The code will need to call on the Excel executable to manipulate Excel workbooks, set visibility of worksheets, unprotect worksheets, clear contents from ranges, as the user (an accountant) interacts with the web app and Excel.

ActiveX might be out of the question due to security reasons (http://ift.tt/1r489Wf) although it is an intranet app.

If this is not possible, are there alternative ideas to achieve similar results?