Avoiding Protected view when opening streamed Excel documents - asp.net

Question

We have an ASP.NET application which dynamically generates Excel documents and streams them to the client, using Response.WriteFile, see code below. Note that the document is deleted once the file has been written to the client. Thus, no documents are ever left on the server.
However, my client's users has now all upgraded to Office 2010, and now the documents will open in "Protected View". In order to edit the document, the user has to click "Enable editing" first. This is considered unacceptable for the users.
The reason that this happens is that streamed documents are placed in the Temporary Internet files, and this is considered a "potentially unsafe location". And documents in such locations are opened in protected view. I am just hoping there is some way to work around this.
Theoretically, I could place the document in a folder which is accessible from the client, and redirect to the document.
This solution is not an option, however. Firstly, since the document would be left on the server, it could be accessible for other users, which is a problem since the documents may contain confidential data.
There are other reasons why this is not a vialable option.
An other theoretical workaround would be to ask all users to disable the setting "Enable protected view for files located in potentially unsafe locations". Naturally, this is not an option either.
So, in short, is there anyway to avoid the documents to be opened in "Protected view" while using the streaming technique described below?
Response.Buffer = true;
Response.Clear();
Response.AddHeader("Pragma", "no-cache");
Response.Expires = 0;
Response.AddHeader("Content-Type", contentType);
Response.AddHeader("Content-Disposition", "attachment; filename=" + proposedFilename);
Response.WriteFile(dstFullPathName);
Response.Flush();
Response.Close();
File.Delete(dstFullPathName);
HttpContext.Current.ApplicationInstance.CompleteRequest();