I have done this successfully several times.
HP Onboard Administrator booting...
Lost Password or Flash Recovery requested
Press L for Lost Password Recovery
Press F for Flash Recovery
Press any other key to reset
Flash Recovery Mode
Obtaining DHCP Address...ENET Speed is 10 Mbps - HALF duplex connection
BOOTP broadcast 1
DHCP client bound to address 10.10.38.240
Done
Please enter the IP address of the tftp server at the next prompt.
Please enter 'serverip':10.10.38.241
Please enter the filename of the ROM image at the next prompt.
Please enter 'bootfile':hpoa480.bin
Downloading the ROM...Done!
Verifying ROM image....Done!
Flashing your Onboard Administrator. This will take several minutes.
Do not power off or reset until the process completes
Flashing...
..
..
..Done!
Flash procedure succeeded.
Restarting the Onboard Administrator.