No secret handshake. These servers being sold on e-bay appear to be custom designed for some ISP or were part of a different release cycle than the one for which drivers are available on Dell's site. If you have forced a BMC update by downloading the BMC firmware from Dell's website, then you have bricked the server. Once bricked the BMC Disable jumper will not work either.
Heed the BMC's warning when it says the firmware does not pass checksum (or something similar to that which appears when you try to flash the firmware.) Its basically telling you that this firmware will not work with this device.
The only way I know of to recover a C1100 that has been bricked is to desolder the BMC EEPROM from the board, program it back to its original firmware code and solder it back on.
Shahid