Unfortunatly I don't think you could and by the way you should notice that it's not recommended to use automation server side, for many reasons.
If you check this
link you can read the following :
“Microsoft does not currently recommend, and does
not support, Automation of Microsoft Office applications from any
unattended, non-interactive client application or component (including ASP,
ASP.NET, DCOM, and NT Services), because Office may exhibit unstable
behavior and/or deadlock when Office is run in this environment.”