I guess the biggest problem is most probably the internal storage (of the eMMC chip) have the same device access name than the gameOS partition on the hdd
My guess is both are dev_hdd0... the reason is because this way sony did not need to implement new devices names for it
*With the flash area (intended to storage firmware) inside the eMMC chip it happens the same... the PS3 mounts a region of the eMMC like if it where NAND (so they are repurposing the device layout from the first PS3 fat models with NAND for the PS3 superslims with eMMC)
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So i guess what you want is not going to be posible in HEN, at least not in a easy way because the responsible to map the devices is the hypervisor so is needed to apply some patches in it
Right now im imagining that there are 2 posible ways to patch it
The hard way... by enabing dev_hdd2 (if i remember right this is a device name that still exists in the hypervisor but is not used in modern firmwares because it was a partition dedicated to install otherOS/linux)
The easy way... by adding the eMMC available blocks to dev_flash (or dev_flash2, or dev_flash3). To achieve this is needed to mess around with the main partition table (first sector of the eMMC storage)
But as far i know nobody has dumped that first sector of eMMC. The PS3 uses the same format for that "first sectors" or other partitions/regions and all them seems to have the same structure... so i bet is going to be standard like the others... so is not a big challenge
The challenge is the fact all this experiments are risky, if you "corrupt" eMMC entirelly (as a consequence of having a malformed first sector in it) the PS3 cant boot because it cant load dev_flash
