Well if your BIOS has locked overclocking, you are out of luck? Since I would assume that means no changing the BCLK (and maybe the multiplier). So if that is not possible then I guess that is that.
You could see if there's similar motherboards from the same manufacturer that do have overclocking enabled and you could possibly flash your motherboards BIOS with a BIOS from one of these other motherboards. But I wouldn't hedge any bets on that working, not to mention if it doesn't, you end up with a borked BIOS and will have to replace it physically on the motherboard.
I'm old school... Because it was done right the first time.