It looks like it's possible for 2008 SP1: previous question.
But what about current newer 2008 R2 version?
We plan to use single 32bit Express edition package to install on every machine. However, on 64bit Windows 7 it produces this error:
FacetWOW64PlatformCheck Determines whether SQL Server Setup is supported on this operating system Failed Setup is not supported in WOW64. This setup program can only be run on a 32-bit system.
/x86 flag for setup.exe doesn't work.
Copying x64/setup folder to the root of installer files doesn't work.