You are getting the default question that pops up on networked machines,
after you select the add-in in the browser. Just answer "No" so it
references the server file. This means it won't be added to the user's
Documents and Settings folder, which I assume is what you want.

I service this exact scenario from home via Remote Desktop, to a company
running add-ins on 12 machines. ...works great!

Regards,
GS