Installing SSMS 2012 after SQL Server 2008 R2 Express was installed (without tools)

Hi everybody,
This is a question in another forum I am frequent. Someone installed SQL Server Express 2008 R2 and he used the wrong exe, so he installed it without tools. Now he wants to install SSMS.
It looks like SSMS 2012 wants to have SQL Server 2012 Express installed first.
Can someone please confirm if it's possible to install just SSMS 2012 after SQL Server 2008 R2 Express was already installed and if possible, guide through the installation steps?
Thanks a lot in advance.
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