On the same machine with SQL Server 2008 R2 Express installed, can the last stand-alone version of the Management Studio be installed? That would be SQL Server 2008 Management Tools. Or does it have to be the latest version that comes with the R2 installer?
You can install the old management console side by side with a newer installation, but I'm not quite sure why you would want to. The newer consoles can connect to the older versions (although this may not be the case with expresss, it's been a long time since I used it).