Now, you can't change the driver - Canon will do that in a few months probably - but you can trick the driver into thinking that it's installing onto Yosemite by temporarily editing the system file. There's actually a very good chance that the Yosemite driver would work prefectly well on El Capitan, it's just that the installer checks a system file containing the OS X version number and checks that against a list - it's purely nominal - the only problem is that 10.11 isn't on that list yet because it wasn't around when the list was made. I checked out the US and EU Canon websites and, indeed, Yosemite is the latest driver.
