Yes that's possible I think. Never used LightSwitch, but if you can create websites with it that run on ASP.Net it's possible.
The Silverlight Multi File Uploader can also work on PHP or any other server side language. Silverlight runs clientside. Only the Handler that receives the files runs serverside and needs asp.net.
If you download the release, you will find a nice sample project. You need to copy a few things to your LightSwitch website:
- HttpUploadHandler.ashx (receives the data)
- silverlight.js (for browser plugin detection)
- ClientBin\mpost.SilverlightMultiFileUpload.xap (the silverlight application)
Then copy the HTML from one of the example pages (slmfu.multi.default.aspx)
Make sure your website can write in the Upload directory. Debug the HttpUploadHandler.ashx if need.