You can just edit your advanced energy settings in the control panel.
Just go Change scheme settings (or what it's called in english) -> Change advanced settings, then in the new window that opens up, go to Energy Settings For The Processor, then Maximum Processor State, and type in a lower value than 100%. Then hit Initialize or Ok on the window.
The names on the alternatives may vary though, I'm not on the English Windows, so it's roughly translated.
That is if you want to do it inside Windows and not in BIOS, it's up to you.