I think it used to work in older versions but no longer AFAIK. It was by running 'explorer.exe' from the Windows/syswow64 folder, and appending '/separate'. I just tried it on the RTM and it just launches as 64bit.
Missing context menu extensions are just a way of life on 64bit Windows, not just W7 I'm afraid. Other apps like 'Unlocker' are affected also as 32bit context menu handlers will not work on 64bit explorer.