In the past when I was back in high school, there seem to be an option to take individual subjects without the need for the extra stringent requirements (and also without the entire diploma). I remembered it was called the certificate program. I also remembered that there was an official IB page on it.
However, I couldn't seem to find it anymore. Has IB phased out individual certificates? There seems to be no official mention of the existence of this route anymore. The last mentions were in forums like College Confidential and are dated quite back.
Loughborough at number one