Unlock the bios? The bios is a collection of code of a specified size. If your motherboard, or very close to it, is available without HP branding there's a chance of flashing to a different bios which will allow you to overclock.
There's also a chance you'll kill your board.
On the other hand, if you're willing to put some time into it, it's definitely possible to rewrite your bios to allow overclocking. This will be difficult and time consuming.