Allow user to download file and filename on client defaults to no extension

Question

I want the user to be able to download a file from a page and have the filename extension in the Save As dialog box to be defaulted to nothing.

This is the code I'm using:

Response.ContentType = "text/plain"
Response.AppendHeader("content-disposition", "attachment; filename=FILE")
Response.WriteFile("C:\Temp\FILE")
Response.End()

FILE is the actual file. It is saved on the server without any extension.

Currently, the "Save As Type" drop down list in the dialog defaults to "Text Document". How can I make it so that it defaults to "All Files"?