Close. You don't even need a Windows service. Just us a serialized queue using MSMQ. Write the queue listener in Javascript and register with COM+. Excel automation on the server is easy if you do it right, and impossible if you do it wrong.
Subsequent to my MSMQ approach, I did a project with Aspose. It's a pretty good toolkit, and I would recommend it over the MSMQ/COM+ complexity - Unless you absolutely have to automate Office, which is sometimes true.
On more recent projects in last ~12 months, I have used OpenXML.
