I actually found out how to do it:

I created a .java file within src/main/java/mycompany and added a method that sets up the property:

    package mycompany;
    
    public class Setup {
    	public void browserSetup() {
    		System.setProperty("webdriver.chrome.driver", "C:\\path\\to\\chromedriver.exe");
    	}
    }

Then, in my test, I imported this as a library:

    *** Settings ***
    Library  Selenium2Library
    Library  automated_tests.Setup

And then invoked the method as a new keyword: `Browser Setup`.

That was it. I ran it and it worked.