Well, I tried it on my own, following
Falseclock's tutorial.
PhoenixTool processed isflash.bin from the linked BIOS (v1.23) flawlessly, but Falseclock's Perl script fails at processing FE3542FE-C1D3-4EF8-657C-8048606FF670_1262.ROM: EFI_HII_PACKAGES() returns an empty array.
I also tried it with isflash.bin from v1.13, which I can use as well as v1.23, but same result.
At first, I wasn't able to dump by BIOS; I tried the platform.ini method and invoking flasher executable with -g switch, both with H2OFFT-Wx64.exe under Windows 7 and with H2OFFT-Sx64.efi in UEFI shell. Using the efi executable with -g switch gave me "Error: IHISI 14h failed. Internal Error Code 0x24. FBTS: Read bios failed".
Then I tried Universal BIOS Backup ToolKit 2.0. Since it stated it couldn't recognise my BIOS, I tried it with size 4096K, and it succeeded. I ran PhoenixTool with that image, which succeeded too, but FE3542FE-C1D3-4EF8-657C-8048606FF670_1262.ROM obtained this way is identical to that I got from isflash.bin.
What I got from PhoenixTool can be downloaded
here. Any advice would be greatly appreciated.