To answer the question "How do I overclock a dual core processor?", I believe the only good answer you'll get is "Get a mothboard that will let you".
Back in the day, the CPU was clocked through some hardware on the motherboard that users could configure through jumpers, dip switches, etc.. In the last decade, I haven't seen a single motherboard that offers that kind of functionality. I believe overclocking must now be done entirely from BIOS. As you said your BIOS doesn't give you access to these kinds of features, you may get lucky with a newer version of your BIOS firmware. Go look up the product page for your motherboard on the Asrock website. If they have newer BIOS revisions, read the change logs and see if any of them introduce this functionality. If so, look in to the process on upgrading your BIOS.
Another option, though unlikely, is if your board is supported by "Coreboot" (an open source BIOS firmware project), then you may gain this functionality by switching to that.
In your question you did say that getting a faster processor isn't an option.. I'm going to assume that means that replacing your motherboard is also out of the question?
Finally, depending on your compiler, you may be able to configure distributed compiling. "distcc" is what you'd use for GCC to that end. Using that you can get multiple machines working on compiling a project and thus build something big faster.
Hope something in there helps you.