How can find out that selected setup file is of SQL server 2008R2 Express x86 version or x64 version?

I am working on the unattended install of sql server 2008R2 using my project's installer where I am prompting user to select the sql server setup file and the sql server is installed from the file selected by user. But I am not able to find out is the selected setup file is of x86 version or x64 version.

For SQL server 2008 R2 there are 2 different setups:

   1. SQLEXPRWT_x64_ENU.exe
   2. SQLEXPRWT_x86_ENU.exe

The file version and product version of both above setup is same i.e. 10.50.1600.1

I can find out it by filename, but I don't want to depend on the filename, because file name can be different [or someone can rename file name e.g. setup.exe] . Please let me know is there any wat to identify that the selected sqlserversetup is of x86 version or x64 version.

Thanks,
Dhiraj