Default Windows 8.1RT esd file, booting 8.1 from VHD

I screwed up my 8.0 install a bit (messed registry hard, office is not working, office setup controller crashes ), and found that I can't shrink my OS partition, because reasons. (seems that some unmovable system files are at the end of partition, diskpart shows that I can shrink about 30gigs, but even 10 fails). I decided to play with OS on VHD. 8.0 works as usual, every "desktop" guide apply here, but it's known that upgrade to 8.1 throws an error that it's impossible to install it on VHD.
It's also known as being not true, as on desktop people are attaching this vdisk to virtual machine, running upgrade, and after booting real machine from it... well, it works. But there's no ARM VM to do that - still I think there's other way to do it.
Seems that very recent version of dism tool from leaked 8.1 2014 upgrade supports ESD files. So what I'm thinking about is upgrading image directly using it, on desktop.
But I'm looking for a way to obtain ESD file. When I started upgrade from Windows Store, in \Windows\Software Distribution\Downloads I found only .exe file responsible for upgrade, but not .esd itself. Any hints where it's located? Or anyone can share it?
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