Boot from the USB and type the command: afudos [filename].rom /p /b /n /x . ECS provides the eBLU (BIOS Live Update) utility.

The motherboard BIOS utility cannot read NTFS or exFAT partitions. Use a drive smaller than 32GB for maximum compatibility.

Is there a single "ECS H61H2MV BIOS Update portable.exe"? No. But is there a portable method that runs entirely off a USB stick without touching your hard drive?