It looks to me like you're on a hiding to nothing, unfortunately. Trying to hack a BIOS to accept an incompatible CPU is always a dodgy proposition. Even if you got it to boot, it might still have lots of other niggly and/or showstopping problems. I think Xeons generally consume more power, for example and that mobo wouldn't be designed for this. It's even possible that the CPU doesn't work anyway, as it's second hand.
I suggest flogging that CPU on eBay and cutting your losses. If you're in a position to, then I suggest just building one from scratch, although it will be expensive and getting hold of a decent graphics card well nigh on impossible nowadays. Cost would be $1000-$2000 depending on how high end you wanna go. Not cheap, I know.
Why did you choose that CPU, anyway?