There are a couple of options that I can come up with to help out and work around the limitation of the web client.
1. You could technically open multiple browser sessions with the same GP Web client so that you could have them h you cannot resize the windows in the Web Client, you could technically open multiple browser windows with the same GP web client user and have them side by side. You may run into issues with it getting confused between the sessions though so I don't think Microsoft would recommend this as an option.
2. You could use SmartView and/or Popdock from eOne Solutions to get "SmartLists" outside of the GP WebClient without having to have GP on the machine itself. SmartView has an External version that runs outside of GP but looks and feels a lot like SmartList. It uses users that you setup for it and can display all your default SmartLists along with SmartList Builder built ones if you have that. Popdock runs in a browser session and is designed to also replace SmartList for GP, but allow you to connect to many of your other systems as well. It has all the default SmartLists built in as well as can bring in any of your SmartList Builder built lists if you have that. If you already own SmartList Builder, it might be worth looking into seeing if you already own SmartView and/or Popdock as they are now sold all together.
3. You could use the built in Refreshable Excel Reports as another option to get the SmartList data in a form where you can have multiple lists open at once. This run outside the webclient, but by default would give you the same data as the default SmartLists do. The Refreshable Excel Reports are included with GP, so you would just need to publish them and setup security to start using them.
With option 2 and 3, you wouldn't have the ability to drill down into the data in the GP Web Client using the Go To's, but at least you would be getting the data in the lists.