You can use
RadProgressArea along with your RadAsyncUpload control to achieve your requirement.
RadProgressArea contains a ProgressTemplate property, which can be
used to fully customize its content and style. For example you can rearrange the
progress elements or create your own progress bar and add custom information regarding the uploaded files. You can also use the OnClientProgressBarUpdating and OnClientProgressUpdating
events in order to modify the look and feel of the progress area to create your
own custom progress gadgets.
Please have a look on this demo on Customization with Templates which deals with a similar scenario.