Not sure if this is new, but latest version supports booting from a wim file using wimboot executable and initrd.
http://grub4dos.chen...ries/downloads/
This can be used to boot a variety of wim files from different folders
\wimboot
\WIN7\bootmgr
\WIN7\boot\bcd
\WIN7\boot\boot.sdi
\WIN7\sources\boot.wim
title WIMBOOT WIN7PE\nBoot WIn7PE from \WIN7 folder kernel /wimboot initrd @bcd=/WIN7/boot/bcd @boot.sdi=/WIN7/boot/boot.sdi @bootmgr=/WIN7/bootmgr @boot.wim=/WIN7/sources/boot.wim
You can also specify the image number, e.g.
kernel /wimboot index=2
initrd syntax is @name1=file @name2=file
also can access files inside initrd file now (maybe for patching linux?)
map /initrd.gz (rd) ls (rd)/