How do I manually throttle the CPU usage of an app?
You could try AppTamer (not free, trial version available). From the AppTamer website:


  Some applications, particularly web browsers and older apps, continue 
  running tasks or animating ads even when they're idle. That uses
  valuable processing (CPU) power, which leaves you with:
  
  Less CPU power for the application you're using, Increased heat and fan
  noise, Reduced battery run-time
  
  Find the culprits and get them under control. With App Tamer, you
  simply do this:
  
  Launch App Tamer and click on its icon in your    menubar, Click on an
  application that's    using a lot of CPU, Tell App Tamer to slow or stop
  the app.