There is nothing built into Web2 to do that. I think it is a restriction from a webpage being able to collect Active Directory information.
You could probably setup some type of script/app on the client machines that populates the data, but there is no way to get the users password from active directory to populate the field with.
I am trying to convince SolidWorks to make it so that the full client could be set to use the web portal as needed. This in theory would fix this issue since the full client can access Active Directory for auto login. Thinking about it more that might require a VPN connection that would also defeat the purpose of accessing through the web portal. Guess I am not being very helpful, so I will stop.