The way I did this before was as follow:
1- Create a unique file name (sys(2015).xls)
2- Copy it to a temporal directory in the web server (ie. \wwwroot\tmpfiles
3- Return that file name as a hyperlink

Since Excel is registered in the client computer, the file will be displayed within the browser. I don't know how clean this is, but it works very nicely. After a while, we ended up creating a routine that cleans up temporal files. Best luck.

Carlos.