RadUpload can pass parameters along with the file (which is where you can pass in what you want)
This link will bring you to the RadUploader documentation on how to attach additional parameters to the upload. http://www.telerik.com/help/silverlight/radupload-features-upload-service-parameters.html
While you're in that documentation, look to the left and scroll down until you see all the features underneath the expanded folders. You will be currently in RadUpload > Features > Upload service Parameters. Take a look at all the other features this control offers you.
Let me know if you need more help than that. If yes, provide me with some more detail on what you are trying to achieve and your project code. I'll help write you a solution to your needs.
Thanks and Good Luck!