From the browser UI, how to identify if VSTO 3.0 is installed in the system?

Question

Objective: From the browser UI, how to identify if VSTO 3.0 is installed in the system?

Use Case: From my ASP.NET web application, i am allowing the user to download a word file which has got "Document Level" vsto 3.0 Add-in. However, if VSTO 3.0 runtime is not installed in the system, the document throws an exception. I wish to do the following scenario:

1. User clicks on the file link.
2. some something (script - vbscript / JavaScript or anything), we need to find out if vsto 3.0 is installed in the system. If not, the user needs to show a popup that VSTO 3.0 is not installed and the ClickOnce URL for installing the VSTO 3.0 runtime needs to be displayed.
3. User would click on the VSTO installer link and the VSTO runtime is installed in the system.
4. the next time, the user wont get the pop-up regarding VSTO 3.0 runtime, and she can successfully download the document containin document level add-in and use the functionality.

Please help!!

Thanks,

Ajit.

Note: Posted in MS VSTO forum too but no answers till yet:

http://social.msdn.microsoft.com/Forums/en-US/vsto/thread/790e366c-3ba5-4690-afab-30185f1895b6