I know this one kept me awake at nights and had me wondering how Google can translate from japanese to english :)
But I eventually managed to find a way… At least for my P35-DS3 board.
This board happily detects and boots any USB stick, as long as the first partition (primary 1) on it is FAT and marked as active. Which is not the case with the ESXi .dd image. The Hypervisor0 partition, although it is physically the first, has the index 4.
You just swap the numbers of partitions 1 and 4 on the stick, without changing the sector layout. Fdisk is the only tool I needed. Write down the initial layout of the partitions, delete and recreate them, only this time make the smallest one primary 1 and the extended one primary 4.
Tested with 3.5U3 and 4.0.
choose x => extra functionality (experts only)
choose f => fix partition order
chhose w => write table to disk and exit
It is easier! :)